Added code quality Rake task.
Added code quality Rake task.

- Separates code quality tasks into a separate `:code_quality ` task
  for the added convenience of being able to run only code quality
  tasks if desired.
- Updates the default Rake task to run the `:code_quality` task if
  defined.
- Code quality tasks are executed first in order to fail builds sooner
  without having to wait for the full test suite to complete.

bkuhlmann/sorter