Update RuboCop to new Gem Version

Update RuboCop to new gem version (0.23.0).
Include New RuboCop file layout specified in [this](https://github.com/bbatsov/rubocop/issues/1050) issue.

Update Rakefile to use new RuboCop class definition.
From Rubocop to RuboCop.

Add new .rubocop_todo.yml file following new RuboCop file structure.

Signed-off-by: "Jake Champlin" <jake.champlin.27@gmail.com>
I'm kind of torn on this. I like how it looks, but @sethvargo taught me to put trailing commas on my hashes so the commit doesn't show changes on lines where nothing really changed. 

Doesn't this present the same problem? If I add a line where the first thing is longer than everything else there, I have to realign everything.