Test/enhancements

I tried to improve the tests by adding a few different things. I felt more confortable doing so using rspec, I hope that's not a problem.

Basically the main change is that requests are made against fixtures (taken from the doc) instead of doing the actual HTTP requests. That makes testing way faster.
All the regexps I used to stub request params, like the different date formats are also taken from the documentation.

If you really want a set of tests that hit the real API, I can add a few, but I think this solution is good enough.

I also added a travis configuration file, so you can enable your repo on travis now.