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 `ENV` variable might become unset. I basically don't care what the error is, though, because the code is intended to be temporarily-lived, for a week or two, then deleted. In that interim, if anything fails, I don't want it to cause any problems in the "build review" lifecycle. Falling back to "false" seemed the safest thing to do to me.