* Add barebones EIP1820 support.

* Update openzeppelin-test-helpers dependency to have ERC1820 support.

* Add tests for ERC1820.

* Improve inline documentation.

* Add changelog entry.

* Update test-helpers, refactor tests to use new helpers.

* Rename ERC1820 to ERC1820Implementer.

* Improve implementer docstring.

* Remove _implementsInterfaceForAddress.

* update openzeppelin-test-helpers to 0.2.0

* Update contracts/drafts/ERC1820Implementer.sol

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

* Fix how solidity coverage is run to allow for free events.

* Fix coverage testing script.