* make _tokenId indexed in Transfer and Approval events
via: https://github.com/ethereum/EIPs/pull/1124/files
* fix: make name() and symbol() external instead of public
* feat: implement ERC721's ERC165
* feat: erc165 tests
* fix: don't use chai-as-promised in direct await
* fix: reorganize to /introspection
* feat: abstract all erc165 tests to a behavior
* feat: disallow registering 0xffffffff
* Rename current ERC721 implementation to BaseERC721
* Implement ERC721 optional & approveAll functionality
* Support for new ERC721 interface
- Tests for new features are pending
- ERC721 is abstract, since it requires metadata implementation
- Move some methods into DeprecatedERC721 contract
- Reorganise base vs full implementation
- Pending tokenByIndex
* Add more tests for ERC721
* Implement suggestions by @dekz
* Update comments in ERC721 contracts
* Implement tokensByIndex extension
- Remove restrictions from mock mint and burn calls
* Add default implementation for metadata URI
This allows token implementation to be non-abstract
* Allow operators to call approve on a token
* Remove gas stipend restriction in call to 721 receiver
* Remove deprecated implementation
We only want to keep the interface, for interacting with already deployed contracts
* Add notice to isContract helper on constract constructors
* Change natspec delimiters for consistency
* Minor linting fixes
* Add constant modifier to ERC721_RECEIVED magic value
* Use 4-params safeTransferFrom for implementing the 3-params overload
* Minor text changes in natspec comments
* Use address(0) instead of 0 or 0x0
* Use if-statements instead of boolean one-liners for clarity
:-(
* Keep ownedTokensCount state var in sync in full ERC721 implementation
* Fix incorrect comparison when burning ERC721 tokens with metadata
* Use address(0) instead of 0 in one more place in ERC721
* Throw when querying balance for the zero address
Required by the spec
* Update links to approved version of EIP721
* Use explicit size for uint
* Remove unneeded internal function in ERC721
Also rename addToken and removeToken for added clarity
* Use underscore instead of 'do' prefix for internal methods in ERC721
* Fix failing test due to events reordering in ERC721 safe transfer
* Fix bug introduced in 74db03ba06
* Remove do prefix for internal setTokenUri method
* Allow transfers to self in ERC721
