Update to follow Guard 2.0 changes

Ignore the messy commits. Updated to follow [changes in Guard 2.0](https://github.com/guard/guard/wiki/Upgrading-to-Guard-2.0#changes-in-guardguard). Added `:verbose` option  to output all concatenated files on concatenation (`"Concatenated #{file_names.join(', ')} to #{output_file}"`) as opposed to `Concatenated #{output_file}`. Been testing for about a week or so and have not had any issues.