This adds the first Librarian: Berkshelf3

This adds the Berkshelf3 librarian to the Knife::Sink namespace. Other librarians will be added so people's different ways of controlling cookbooks can, hopefully, be supported.

Of course, patches welcome!
add missing files to repo

- knife-sink.gemspec
- lib/knife-sink.rb
add extra comment line to class docs
add Rubocop configs, including temporary todo file
Merge pull request #1 from theckman/add_berkshelf3_librarian

This adds the first Librarian: Berkshelf3