Rubocop Sample config file and exempted cops in existing code

Take one or take both commits, but something to look at.

I will write something later in the README file to give hints on using Rubocop with exercise submissions.

re: #64 
What do you think of disabling both AbcSize and MethodLength globally for this repo?

Since the rubocops will be applied to the test suites, I don't really see size and method length as good guidelines.