implementation of branch date check

this is the work I've done about the issue #37

I'm a php developer, I (really) love ruby but I'm definitely not a full time ruby developer. So...take this as an attempt. The tests are there. I've changed the CommitTime class signature by accepting only the timestamp.

On my machine everything works fine, and the tests are green. Maybe some work can be done to do some better checks on the time ago...for example we can prefer 5w over 1mo.

let me know what you think...