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/
I find this style of heredoc harder to read than something like:
```ruby
code = <<-CODE.strip_heredoc
  class FooBar
    foo: ->
      "bar"
CODE
expect(violations_in(code)).to be_any { |m| m =~ /inconsistent/ }
```