Add CoffeeScript support

* Use [CoffeeLint] to keep to a community-supported open source standard.
* Memoize the HTTP requests.
* Add flag to enable CoffeeScript
* Rename `Null` style guide to `Unsupported`

[CoffeeLint]: http://www.coffeelint.org/
@gylaz Do you think we should maintain parity and allow users to enable or disable Hound for Ruby?