Introduce example to run validation of of rubocop rules

[miry]

There are sometime misconfigured Readme and Rubocop.
Make sure Rubocop correctly work, propose to have a file with
good and bad cases.

Started work, but would like to get feedback, before migrate Readme examples to ruby file.

Partialy covers #189

[sambostock]

I wonder if it would be possible to inline these in the README itself and then run Rubocop against that. Maybe we could look for ```ruby code blocks that have # good or # bad at the top.

Moving them to a seperate file just increases the synchronization problem, as we'd now have to keep three files in sync ( README.md, examples/sample.rb, and rubocop.yml) instead of just two.

[miry]

@sambostock you read my mind. Have not investigated though. Probably it is not hard to write Markdown parser and feed to rubocop tests.

[volmer]

It would be really nice to be able to run RuboCop against the examples we have in the Readme. That would be better than having a separate Ruby file with code samples. Would you be interested in working on a parser for that?

[miry]

It would be interesting.