Add CoffeeScript support

* Use [CoffeeLint] to keep to a community-supported open source standard.
* Propose a `.hound/ruby.yml` and `.hound/coffee.json` naming convention.
* `.hound.yml` will still work (backwards compatible) but would now be
  considered legacy / deprecated.

[CoffeeLint]: http://www.coffeelint.org/
They used to be passed in but then as the requirement changed so that we need to access the `pull_request` from the style guides, it seemed like a smell to me to have a method signature like `new(pull_request.pull_request_files, pull_request)`.

What do you think? What's the advantage of passing them in?