Coverage

Hey :) 
* I've tried to integrate separated coverage and for this matter I had to split the tests into separate files.
* I also added travis config. The repository should be added to travis-ci, right? And the badge.
* Some code style follow-ups and your favorite `indexes` :)

Hope, I didn't miss anything. If so, let me know.

I think we can better put this to `devDeps` and include to the `travis` npm task?