Improved test coverage

- Got rid of JSXTransformer in test suite since it is not needed
- Simplified firebaseRef validation (we ran into a Node bug with this
old validation in GeoFire so we should change it here as well)
- Added a bunch of tests to improve code coverage
- Simplified existing tests
Fixed issue with second _bind() test
Updated change log for upcoming 0.2.1 release
Added error codes to all errors and updated test suite
Merge pull request #16 from firebase/jw-testing

Improved test coverage