adds git.status and its tests

Fixes #36 
 - adds `lib/status.js` and its tests

I had a hard time on that big test file, do you mind if I split the tests on separate files? On a separate PR that is of course? 

I'll keep the `clone` begining and `rimraf` end the middle part woud be a `fs.readdirSync` similar to [these](https://github.com/stringparser/batch-these/tree/master/test) ones.