Check CoffeeScript using CoffeeLint

At my company we have quite a lot of CoffeeScript code, and I would love for Hound to be able to check CoffeeScript code too, not just Ruby. The current implementation only checks four rules, however if more rules are added to CoffeeLint they should be fairly straight-forward to add to Hound. The implementation does support customization through a `coffeelint.json` file, though.

TODO:
- [x] Update `app/views/application/configuration.haml`?
There's talk about providing our own configuration syntax, instead of using the underlying gem's. This is because RuboCop has recently changed the syntax to their configuration, and this will break many people's config via `.hound.yml`. We're still discussing the right way to handle this, but we might hold off on adding another gem's configuration until we figure out the right way to handle this.