Use coffeelint-stylish reporter and document configFile option.

Hi, with this pr we have
* [coffeelint-stylish](https://github.com/janraasch/coffeelint-stylish) doing *pretty* reporting and
* a little section in the `README.md` about the `configFile` option, which was introduced lately.

This fixes #29 in my opinion and provides proof that #13 can be closed as well.