Switched to CLIEngine per #34.

Had to add a simple formatter since CLIEngine just returns an object
with the lint info.
So, as far as I could tell, there are no reporters for CLIEngine. From the eslint [docs](http://eslint.org/docs/developer-guide/nodejs-api.html):

> Once you get a report object, it's up to you to determine how to output the results.

Reporters or formatters aren't mentioned anywhere that I could see. If you can point me in the right direction I'll make the appropriate changes.