Add the MothereffingBases.[] method

- Added the `[]` method for brevity and clarity
- Polished the README with updated documentation
- Fixed an issue that made yard sweat on fenced code blocks in the README, now
  they works fine and the documentation on rdoc.info is ok
Add support for Coveralls

- Added Coveralls as a dev dependency and added the code to make it work to
  `test_helper.rb`
- Added a Coveralls config file (.coveralls.yml)
- Added the Coveralls badge in the README