Rails 4 support

- Fixed annoying rubygems warning about the source.
- Added Rails 4.0.0 and 4.0.1 to appraisals.
- Added a new file for 4.0 with the patches.
- Updated docs to reflect Rails 4 support.
- Removed test-related files from gem build files list. Those are required only for the development environment.
- All specs passing for all versions in Appraisal.