* Update gsn_advanced.adoc

Line 15 - where it says, "prevent malicious users from spending the transactions subsidy", with transactions subsidy, is it supposed to be possessive "transaction's subsidy" or is the plural in the wrong place "transaction subsidies"?

Line 176 - where it says "or it is not allowed to spend that amount". Is IT referring to the sender/person or the tx? If IT refers to a person, then change to "or they are not allowed..." for gender neutral.

Line 213 - Where it says, "Please not how the gas cost estimation", a verb is missing, please what?

* Update gsn_advanced.adoc

Apply suggestions by Amy

* switch to using Context internally

* add context import

* Add smoke test to make sure enabling GSN support works

* Update test/GSN/ERC721GSNRecipientMock.test.js

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

* Upgrade truffle

* add missing awaits

* Revert "Upgrade truffle"

This reverts commit f9b0ba9019650fdbf8919a33e6fba834689e6b04.

> openzeppelin-solidity@2.3.0 lint /home/luiserebii/github/openzeppelin-solidity
> npm run lint:js && npm run lint:sol

> openzeppelin-solidity@2.3.0 lint:js /home/luiserebii/github/openzeppelin-solidity
> eslint .

> openzeppelin-solidity@2.3.0 lint:sol /home/luiserebii/github/openzeppelin-solidity
> solhint --max-warnings 0 "contracts/**/*.sol", alongside some minor grammatical corrections

* Add base Context contract

* Add GSNContext and tests

* Add RelayHub deployment to tests

* Add RelayProvider integration, complete GSNContext tests

* Switch dependency to openzeppelin-gsn-provider

* Add default txfee to provider

* Add basic signing recipient

* Sign more values

* Add comment clarifying RelayHub's msg.data

* Make context constructors internal

* Rename SigningRecipient to GSNRecipientSignedData

* Add ERC20Charge recipients

* Harcode RelayHub address into GSNContext

* Fix Solidity linter errors

* Run server from binary, use gsn-helpers to fund it

* Migrate to published @openzeppelin/gsn-helpers

* Silence false-positive compiler warning

* Use GSN helper assertions

* Rename meta-tx to gsn, take out of drafts

* Merge ERC20 charge recipients into a single one

* Rename GSNRecipients to Bouncers

* Add GSNBouncerUtils to decouple the bouncers from GSNRecipient

* Add _upgradeRelayHub

* Store RelayHub address using unstructored storage

* Add IRelayHub

* Add _withdrawDeposits to GSNRecipient

* Add relayHub version to recipient

* Make _acceptRelayedCall and _declineRelayedCall easier to use

* Rename GSNBouncerUtils to GSNBouncerBase, make it IRelayRecipient

* Improve GSNBouncerBase, make pre and post sender-protected and optional

* Fix GSNBouncerERC20Fee, add tests

* Add missing GSNBouncerSignature test

* Override transferFrom in __unstable__ERC20PrimaryAdmin

* Fix gsn dependencies in package.json

* Rhub address slot reduced by 1

* Rename relay hub changed event

* Use released gsn-provider

* Run relayer with short sleep of 1s instead of 100ms

* update package-lock.json

* clear circle cache

* use optimized gsn-provider

* update to latest @openzeppelin/gsn-provider

* replace with gsn dev provider

* remove relay server

* rename arguments in approveFunction

* fix GSNBouncerSignature test

* change gsn txfee

* initialize development provider only once

* update RelayHub interface

* adapt to new IRelayHub.withdraw

* update @openzeppelin/gsn-helpers

* update relayhub singleton address

* fix helper name

* set up gsn provider for coverage too

* lint

* Revert "set up gsn provider for coverage too"

This reverts commit 8a7b5be5f942002710cba148f249cb888ee8e373.

* remove unused code

* add gsn provider to coverage

* move truffle contract options back out

* increase gas limit for coverage

* remove unreachable code

* add more gas for GSNContext test

* fix test suite name

* rename GSNBouncerBase internal API

* remove onlyRelayHub modifier

* add explicit inheritance

* remove redundant event

* update name of bouncers error codes enums

* add basic docs page for gsn contracts

* make gsn directory all caps

* add changelog entry

* lint

* enable test run to fail in coverage

* GSN Advanced guide

* Tweaks

* Apply suggestions from code review

Changed word from Destoys to Destroys in line number 220.
https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/token/ERC20/ERC20.sol#L220

Need review. Thanks 👍

Fix typo

* replace readme badge

* remove travis config

* move to codecov

* add codecov config

* fix coverage running

* GSN basics guide (#1847)

* Fix linter error

* Initial draft for basic GSN guide

* Add CustomerAcquisitonCost link

* Review 'gas costs' phrasing

* Rename relay to relayer

* Apply suggestions from code review

Co-Authored-By: Santiago Palladino <spalladino@gmail.com>

* Improve transition to contract usage explanation

* Improve payment section phrasing

* Apply suggestions from code review

Co-Authored-By: Andrew B Coathup <28278242+abcoathup@users.noreply.github.com>

* Apply more review suggestions

* Add code

* Add unreleased warning

* GSN Docs Tweaks (#1860)

* Adjusts links

* Adjustments

* Update gsn.adoc

Fix typo

* Adjusts copy and links for GSN guide (#1865)

* Adjusts copy and links

* Formats links

* Adds website link

* remove attach_workspace

* leave default working_directory

* use npm ci for installing deps

* rename dependencies job

Fix typo

* Add circlci, remove .travis.yml. Fixes #1839.

* Fix circleci config

* Add slack notification

* Add circleci status

* Fix config.yml, we don't need separate truffle image and instances.

* Matches oz-sdk node version

* Seems node:10.13 doesn't work for CircleCI either

* Remove npm update in circleci

* CircleCI use package-lock.json as cache key and install only the lock version

* Add back travis.yml

* Rename job build to test

* CircleCI requires that job to be called build instead of test or build_and_test

* Fix the way to run jobs

* Fix CircleCI

* Change back to npm install

* Add workflow and split into tasks

* Add workspace

* Restore cache

* update readme circleci instructions

* make step name more accurate

* Imporvement: functions in SafeMath contract overloaded to accept custom error messages.

* CHANGELOG updated, custom error messages added to ERC20, ERC721 and ERC777 for subtraction related exceptions.

* SafeMath overloads for 'add' and 'mul' removed.

* Error messages modified.

* Update CHANGELOG.md

* added _safeTransferFrom function

* added safeMint functions

* added package-lock.json for consistency, don't know why it changes

* added initial suggestions/modifications

* change _safeTransferFrom to internal, reverted package-lock.json to original, and changed ERC721Pausable to override _transferFrom instead of transferFrom

* included tests for safeMint functions

* modified safeMint tests to be on ERC721Mock contract

* added safeMint to ERC721Mintable & respective test to ERC721MintBurn.behavior.js

* Rename package and repository name from docs and scripts

* undo root package rename

* add @openzeppelin/contracts as subpackage with release automation

* synchronize @openzeppelin/contracts version

* remove private field from package.json

* make file patterns absolute

* change wording of a comment

* use a saner version script

Add: Interface names should have a capital I prefix.

* add OwnableCautious with associated mock and tests

* extraneous comma removal and cleanup

* remove non-documentation changes from branch

Change URLs to openzeppelin.com

Update URLs and names to OpenZeppelin and OpenZeppelin Contracts

Update URL to openzeppelin.com

* update readme with new branding

* update readme text with new branding and links

* add newer link to api stability document

Squashed commit of the following:

commit fcf35eb806100de300bd9803ce3150dde1ecc424
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Wed Jul 17 17:16:04 2019 -0300

    remove all docsite dependency

commit eeaee9a9d43d70704f6ab17b5126ddbd52b93a50
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Wed Jul 17 17:15:23 2019 -0300

    update solidity-docgen

commit f021ff951829ea0c155186749819403c6b76e803
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Wed Jul 17 17:05:06 2019 -0300

    update docsite script for new setup

commit ff887699d381cfbbe3acf1f1c0de8e22b58480f3
Merge: c938aa1d 84f85a41
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Wed Jul 17 16:46:46 2019 -0300

    Merge branch 'master' into antora

commit c938aa1d9ed05ac83a34e2cebd8353f8331ad6d6
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Tue Jul 16 18:24:29 2019 -0300

    make component name shorter

commit 5bbd6931e02cbbd8864c82655ad0f390ceead5f3
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Wed Jul 10 20:16:17 2019 -0300

    add all info to docs templates

commit 39682c4515d7cf0f0368ed557f50d2709174208a
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Wed Jul 10 20:13:49 2019 -0300

    fix npm docsite script

commit 7ae46bd4a0437abf66150d54d05adf46e3de2cab
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Wed Jul 10 18:48:05 2019 -0300

    convert inline docs to asciidoc

commit cfdfd3dee4b4bf582fde22c8cb6e17a603d6e0c8
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Wed Jul 10 17:34:52 2019 -0300

    add missing contract names in readmes

commit 15b6a2f9bfb546cf1d3bf4f104278b118bf1b3f4
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Wed Jul 10 17:16:47 2019 -0300

    fix script path

commit 80d82b909f9460d1450d401f00b3f309da506b29
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Wed Jul 10 17:13:53 2019 -0300

    update version of solidity-docgen

commit a870b6c607b9c2d0012f8a60a4ed1a1c8b7e8ebd
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Wed Jul 10 17:03:53 2019 -0300

    add nav generation of api ref

commit 069cff4a25b83752650b54b86d85608c2f547e5e
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Wed Jul 10 16:32:14 2019 -0300

    initial migration to asciidoc and new docgen version

commit 55216eed0a6551da913c8d1da4b2a0d0d3faa1a8
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Tue Jun 25 20:39:35 2019 -0300

    add basic api doc example

commit 0cbe50ce2173b6d1d9a698329d91220f58822a53
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Tue Jun 25 19:31:31 2019 -0300

    add sidebars

commit 256fc942845307258ac9dc25aace48117fa10f79
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Tue Jun 25 15:22:38 2019 -0300

    add page titles

commit f4d0effa70e1fc0662729863e8ee72a8821bc458
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Tue Jun 25 15:19:41 2019 -0300

    add contracts index file

commit b73b06359979f7d933df7f2b283c50cb1c31b2a0
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Tue Jun 25 15:14:52 2019 -0300

    fix header levels

commit fb57d9b820f09a1b7c04eed1a205be0e45866cac
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Tue Jun 25 15:11:47 2019 -0300

    switch format to preferred asciidoctor format

commit 032181d8804137332c71534753929d080a31a71f
Author: Francisco Giordano <frangio.1@gmail.com>
Date:   Tue Jun 25 15:05:38 2019 -0300

    initialize antora component and convert docs to asciidoc