Add more usage instructions to README

Fix identation and some linter warnings

Remove ethpm.json

The package is not registered in ethpm at the moment. This file was an
artifact leftover from vanilla openzeppelin. This PR removes it, until
we decide to register openzeppelin-eth on ethpm.

Fix example in README.md

Remove initialize from ERC721Full

Following d75ba162 ERC721 should not initialize their parents.

v2.1.2

v2.1.1

* Now compiling using truffle 5.

* Migrated some test files, missing BN scientific notation usage.

* Now using BN time values.

* Migrate ERC20 tests.

* Migrate all ERC20 tests.

* Migrate utils, payment and ownership tests.

* All tests save ERC721 migrated.

* Migrated ERC721 tests.

* Fix lint errors.

* Delete old test helpers.

* Fix remaining crowdsale tests.

* Fix signature bouncer tests.

* Update how constants is used.

* Compile script pre-removes the build dir.

* Fix SafeMath tests.

* Revert "Compile script pre-removes the build dir."

This reverts commit 247e7451135d33c056a126e9e5fd77a24348018d.

* Fix linter errors.

* Upgrade openzeppelin-test-helpers dependency.

* Update openzeppelin-test-helpers dependency.

* Define math constants globally.

* Remove unnecessary ether unit.

* Roll back reduced ether amounts in tests.

* Remove unnecessary toNumber conversions.

* Delete compile script.

* Fixed failing test.