Squashed commit of the following:

commit 06243c3e8e86074ff8e9e3f22b7829a2c315d707
Merge: 991882ec 99373558
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Thu May 23 18:15:37 2019 -0300

    Merge branch 'api-docs' into api-docs-merge

commit 991882eca5bb8a3391995154bfb9d53d8a69cb4f
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Thu May 23 18:08:02 2019 -0300

    manually apply docs changes and renamings

commit fa1f6e97dd67a76c3cd828d0a5e19b4ac6c37acb
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Thu May 23 17:36:03 2019 -0300

    move functions to new order

commit 99373558e3af4905d29bc6f3f542ba93d28a24ab
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Thu May 23 16:23:40 2019 -0300

    add missing docs links

commit d180d6c36a6f5460e85473ee5a18992d1449a6ff
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Thu May 23 16:14:12 2019 -0300

    update solidity-docgen dependency

    fixes uri encoded links

commit faab0e50da91cd2f0a409e3ad32e2db127ad319a
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Thu May 23 16:05:03 2019 -0300

    update openzeppelin-docsite and solidity-docgen dependencies

    add visibility specifiers

commit ef305268bb2735e488e35d16819a4b432b3a35e3
Author: Nicolás Venturo <nicolas.venturo@gmail.com>
Date:   Thu May 23 15:36:45 2019 -0300

    Fix guide links.

commit 339b20dbfa2d5f6ea02e63c2f3fdcba0fe879c3c
Author: Nicolás Venturo <nicolas.venturo@gmail.com>
Date:   Thu May 23 13:37:51 2019 -0300

    Fix typos.

commit 6c7b97460578b9eea90b53c280454e361f8f0052
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Thu May 23 15:26:29 2019 -0300

    fix utilities guide links

commit 0e7692a8fd8516a11becc4121d77d792439600b1
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Thu May 23 15:23:19 2019 -0300

    update solidity-docgen dependency

commit ebb8a8651516ece21736c6c3b2577eb1b3487651
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Thu May 23 15:15:01 2019 -0300

    fix utilities guide links

commit 5ec47d62785e1d6e5f8e91edca58f2dc7f87d7a3
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Thu May 23 15:14:49 2019 -0300

    fix escrow docs ordering

commit cdcdc909b16f219a9a3272036b6a8f21e34b48ef
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Thu May 23 13:35:07 2019 -0300

    add wip notice

commit 987e2951ae93211c8c70c8288e30573555c57830
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Thu May 23 13:09:35 2019 -0300

    update openzeppelin-docsite dependency

    fixes links to old versions

commit b00d22c0affac2e2108df8b773dfa1706afcb44e
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Thu May 23 13:09:28 2019 -0300

    fix guide links

commit f112a9400c5e5ad495c8e0fdb972e26987b34244
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Wed May 22 20:42:37 2019 -0300

    update docsite

commit 68aacdd56a29e35a84f6732f9293612bbcaf7520
Author: Nicolás Venturo <nicolas.venturo@gmail.com>
Date:   Wed May 22 20:00:39 2019 -0300

    ERC20Capped

commit 4edce78bab2c6d140f3ea3f33db71e92ca4d8aaf
Author: Nicolás Venturo <nicolas.venturo@gmail.com>
Date:   Wed May 22 19:52:30 2019 -0300

    Unnecessary polish on token docs.

commit 2a4c91cf49c2736dc09c1c03cf383911def1a1b2
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Wed May 22 19:20:05 2019 -0300

    rename guides

commit 61dd818ea76d4c170c4ab175c6be0d6067d21a29
Author: Nicolás Venturo <nicolas.venturo@gmail.com>
Date:   Wed May 22 17:04:09 2019 -0300

    ERC1820 docs.

commit 77b5f0353123b76358dc6d86bdc646c86c9b0bea
Author: Nicolás Venturo <nicolas.venturo@gmail.com>
Date:   Wed May 22 16:17:34 2019 -0300

    Introspection and ERC165.

commit 76641a253b3b70279802c5134dd107532eea4b2c
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Wed May 22 17:59:53 2019 -0300

    update docgen

commit 7be98bc3fbd3566231f943f01b9acb58567d755b
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Wed May 22 17:23:50 2019 -0300

    update solidity-docgen

commit f7268e6e010f8ef9ac83df241a803f91efc08c0c
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Wed May 22 16:58:31 2019 -0300

    update docgen

commit 2a8c7a378e8962a5baeb334b2492815f05075f98
Author: Nicolás Venturo <nicolas.venturo@gmail.com>
Date:   Wed May 22 14:36:35 2019 -0300

    Util docs.

commit 327ae8ff45a1a523c7591bf4996c4a9b52d7ec7a
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Wed May 22 13:08:50 2019 -0300

    add missing drafts

commit 5e7f71335ac8423c0e363ae8c7ad9b2977f202f8
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Wed May 22 12:47:41 2019 -0300

    tweak ierc20 docs

commit cd0e86a0b712f74ffd406e072d4b1fbf4dd2c176
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Wed May 22 12:46:45 2019 -0300

    add some erc721 docs

commit e081184159417f71da14bc0fc110b7b11e29d75d
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Wed May 22 12:41:46 2019 -0300

    update docsite

commit 0beb75784022419d47123c2a9fe7a5f1eb87f9b2
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Wed May 22 12:22:27 2019 -0300

    correct drafts structure

commit 2e94b287c7cead7a6c0603205670566461c31abb
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Wed May 22 11:56:25 2019 -0300

    fix docsite-start script

commit 0fa4160484309d0851584fe57c0d81a3600977db
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Wed May 22 11:47:44 2019 -0300

    improve docsite start script (automatically watch docgen)

commit 9d571897cc03bee92035964cf7a2cfeda1e2f690
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Wed May 22 11:30:37 2019 -0300

    update solidity-docgen

commit 82980f5aefbdfb8a9815a3b7b0e88e970b65dd5d
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Tue May 21 19:15:13 2019 -0300

    edit docs for Secondary

commit 00d7a005b0530bee730b77a1b69a95f1b4ffe315
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Tue May 21 19:15:13 2019 -0300

    edit docs for ownable

commit b0c4c2bdf83eca5d4a71792daac603236733d46e
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Tue May 21 18:27:13 2019 -0300

    change title of Math section

commit deb788583f191780e55b7f673520eaf13a5c7e23
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Tue May 21 18:26:59 2019 -0300

    capitalization

commit f2bcf85d343ea4a0739fe22a77b1e22c2296ddea
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Tue May 21 18:26:06 2019 -0300

    edit docs for Pausable

commit 73ba0cf43dbb44c39c1bf2ee63ef9fe558faa919
Author: Nicolás Venturo <nicolas.venturo@gmail.com>
Date:   Sat May 18 19:08:06 2019 -0300

    Crypto docs.

commit 9d6fc6223f51cf2321b2e3217c512579654c3917
Merge: 7e21f8f7 9f1cec12
Author: Nicolás Venturo <nicolas.venturo@gmail.com>
Date:   Fri May 17 17:23:15 2019 -0300

    Merge branch 'api-docs-777' into api-docs

commit 9f1cec12e3351fb1b5fc0b59f5ded39928064a56
Author: Nicolás Venturo <nicolas.venturo@gmail.com>
Date:   Fri May 17 17:22:54 2019 -0300

    ERC777 done.

commit 7e21f8f7b6982d2f92df302cdf6ec62522d8ffff
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Fri May 17 16:39:47 2019 -0300

    add math docs

commit f18d1f17023b6e5b42ae04fc38aa1170e6863864
Author: Nicolás Venturo <nicolas.venturo@gmail.com>
Date:   Thu May 16 20:01:46 2019 -0300

    First draft of ERC777 docs.

commit 985c5d305329fd9d400120d86dce5c386e19cd50
Author: Nicolás Venturo <nicolas.venturo@gmail.com>
Date:   Thu May 16 19:14:32 2019 -0300

    Final draft for IERC777.

commit bf53f133d987b67f938a329e6d659ba3483aab0b
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Thu May 16 19:13:37 2019 -0300

    more work on ERC20 api docs

commit b7c250b7cb4669448cfab5535c4ff70b94a15635
Author: Nicolás Venturo <nicolas.venturo@gmail.com>
Date:   Thu May 16 17:08:47 2019 -0300

    Fix typo.

commit 197bbfbfc67a09607ead492b834879c62b3d905a
Author: Nicolás Venturo <nicolas.venturo@gmail.com>
Date:   Thu May 16 17:05:14 2019 -0300

    Initial draft of IERC777.

commit 7dc3b55161c860437a8f13a2ce5808b1c3dd70a2
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Thu May 16 11:58:32 2019 -0300

    add payment docs structure

commit da16fc4480243181e58c3440e977e76a91a1839a
Author: Nicolás Venturo <nicolas.venturo@gmail.com>
Date:   Thu May 16 16:05:33 2019 -0300

    Initial ERC777 docstrings.

commit 9f6a7e35bd2f045e6063ca2f93c67b792c0ef47c
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Wed May 15 22:13:17 2019 -0300

    partial pass through ERC20 docs

* update truffle to include bugfix

* change prepack script to prepare

* add npx in compile script

* fix for older node

* rename script file to prepare

* Fix transferFrom not updating allowance before calling receiver.

* Fix from being passed as operator.

* Add requirement of non-zero from to ERC20 transfer.

* Add test for transferFrom zero address to behavior.

* Create ERC20.transfer behavior.

* Add tests for _transfer.

* Add changelog entry.

* Fix linter error.

* Delete repeated test.

* Fix hardcoded error prefix.

* Update CHANGELOG.md

Co-Authored-By: Francisco Giordano <frangio.1@gmail.com>

* Address review comments.

* improve prepack script

* remove .npmignore

* make prepack use pkg.files

* fix linter errors

* Moved ERC1820 related contracts out of drafts and into introspection.

* Moved ERC777 related contracts out of drafts and into token.

* inline keccak256 result

* Update ERC777.sol

* switch hex constant style

* Update ERC777.sol

* Add ERC20 compatibility.

* Reusing ERC20 tests for ERC777.

* Improve documentation.

* Add changelog entry.

* Improved ERC20 behavior tests.

* Add revert reasons to ERC777.

* ERC20 methods allow sending tokens to contracts with no interface.

* Register ERC20 interface.

* Add comment about avoidLockingTokens.

* Improve revert reason string.

* Make ERC777 implement IERC20.

* Fix test revert string.

* Remove unnecesary require.

* Add private _transfer.

* Update contracts/drafts/ERC777/ERC777.sol

Co-Authored-By: nventuro <nicolas.venturo@gmail.com>

* Update private helper names.

* Hardcode ERC777 granularity to 1, remove tests.

* Add clarifying title comment.

* update truffle to 5.0.14

* fix setup to test with solc-nightly

* switch to npx in script/test.sh

* please the linter

* rename build to prepack

* move download of nightly build to a compile script

* make compile script executable

* Error handling in ERC20 and ERC721

* Added message string for require.

* Fixed solhint errors.

* Updated PR as per issue #1709

* changes as per #1709 and openzeppelin forum.

* Changes in require statement

* Changes in require statement

* build pipeline fix

* Changes as per @nventuro's comment.

* Update revert reason strings.

* Fianal update of revert reason strings.

* WIP: Updating reason strings in test cases

* WIP: Added changes to ERC20 and ERC721

* Fixes linting errors in *.tes.js files

* Achieved 100% code coverage

* Updated the test cases with shouldFail.reverting.withMessage()

* Fix package-lock.

* address review comments

* fix linter issues

* fix remaining revert reasons

* Add a vault to PostDeliveryCrowdsale.

* Add changelog entry.

* Apply suggestions from code review

Co-Authored-By: nventuro <nicolas.venturo@gmail.com>

* Rename TokenVault.

* add solhint ignore directive

* Bump Solidity version to 0.5.7

* Add changelog entry.

* initial docsite setup

* switch from pushd to cd

* install and set up solidity-docgen

* use the docsite branch next for now

* make it clear that env var is a repository

* add a clarifying comment about a relative path

* change relative to absolute path in docsite script

* add docgen script

* add first few READMEs for contract documentation

* update solidity-docgen

* add docsite as dependency and adjust script

* update openzeppelin-docsite

* update solidity-docgen

* remove dummy text

* update docgen and docsite

* update openzeppelin-docsite

* add netlify.toml

* udpate tokens guide for 2.2

* add DOCUMENTATION.md

* Update docs/learn-about-utilities.md

Co-Authored-By: frangio <frangio.1@gmail.com>

* fix PaymentSplitter docs wording

* update solidity-docgen

* add missing ERC20 contracts

* update solidity-docgen

* trigger deploy with cleared cache

* update solidity-docgen

* update openzeppelin-docsite

* remove travis docs setup

* update openzeppelin-docsite

* switch to published solidity-docgen

* Create autoamtic release script.

* Add changelog update date script.

* Improve release scripts.

* Apply suggestions from code review

Co-Authored-By: nventuro <nicolas.venturo@gmail.com>

* Apply suggestions from code review

Co-Authored-By: nventuro <nicolas.venturo@gmail.com>

* Remove moment dependency.

* Fixes/Improves constants inline documentation.

* Fixed solhint error.

* Moved the comment before the variable

* IERC777 from specs, constants returned, up to defaultOperators. (#1159)

* IERC777 oprarator approvals (#1159)

* ERC777 oprarator approvals fixes and tests

* IERC777 send and receive with ERC820 (#1159)

* ERC777 Add burn functions and fix send functions (#1159)

* ERC777 Make expectEvent compatible with web3.js 1.0 (#1159)

* ERC777 Add ERC820 deploy script (#1159)

* ERC777 Complete implementation of ERC777 (#1159)

This implementation conforms to the current EIP

* ERC777 Update ERC820 Registry contract to final version (#1159)

* ERC777 Move contracts to 'drafts' folder (#1159)

* ERC777: Update to ERC1820 registry and linter error fix (#1159)

* ERC777: implement recent changes of EIP777 (#1159)

* ERC777 Fix formatting (#1159)

* ERC777 Update to solc 0.5.2 (#1159)

* ERC777 Fix travis CI errors (#1159)

* ERC777 Fix linter errors again... (#1159)

* ERC777 Fix unit test (#1159)

* ERC777 Fix unit test again (#1159)

* Remove extra newlines.

* Rename ERC777Base to ERC777.

* Remove 'Token' from contract names.

* Replace ops for operators.

* Move operator check out of _send.

* Remove ERC777Burnable.

* Remove ERC1820Client, now using the interface directly.

* Minor internal refactors in contracts.

* Delete extra test helpers.

* Simplified tests.

* Add basic 777 tests.

* Add granularity send test.

* Add first operator send tests.

* Add burn tests.

* Refactor send and burn tests.

* Improve send burn refactor.

* Greatly improve test module.

* Burn instead of send removed tokens.

* Add operator tests.

* Improve send tests under changing operators.

* Refactor and merge send and burn tests.

* Add missing and not-implemented tests.

* Make _burn private.

* Fix typo.

* Greatly improve tokensToSend tests.

* Refactor hook tests.

* Fix hook tests.

* Update openzeppelin-test-helpers and ERC1820 address.

* Fix natspec indentation.

* Make interface functions external.

* Remove redundant private revoke and authorize functions.

* Improved readability of if statement.

* Remove unnecessary asserts.

* Add non-one granularity test.

* Fix hook call order in _mint.

* Fix _mint not reverting on failure to implement tokensReceived.

* Remove special case in operatorFn when from is 0.

* Refactor ERC777SenderMock.

* Add tokensReceived tests.

* switch to updated ganache-cli-coverage fork

* Fix linter errors.

* Add mint tests.

* Fix linter errors.

* Fix tests.

* Update test/drafts/ERC777/ERC777.test.js

Co-Authored-By: nventuro <nicolas.venturo@gmail.com>

* Add changelog entry.

* removed unnecessary require

* build pipeline fix

* kept as it is

* Added require

* removing unused variables

* undeleting the _

* replacing all instances of from: anyone with from: other

* replacing all instances of from: anyone with from: other

* replacing all instances of from: anyone with from: other

* changing anyone to other

* changing anyone to other