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/
> The tests still pass after removing the `if` (and the `compact`).

Okay. I think that's more a sign of missing test coverage than anything else.

> I also can't think of a case where line 12 would return a falsey value.

My thinking here is that CoffeeLint needs to run on the whole file. So, I believe it will collect violations in parts of the file that aren't in the diff. Therefore, we need to restrict the violations to just the changes in the PR. I will try to prove this with specs, though.