drone.io CI

I integrated drone.io as a replacement to executing "python test.py" when submitting a pull request.

I omitted http://docs.drone.io/databases.html#redis as there are no unit tests for sample_app.py yet.

Also the drone.io Badge will need to be amended to reflect the git branches of https://github.com/Instagram/python-instagram rather than my forked repository.

"python tests.py" output below (yes this would be redundant if this pull request is merged):
```
..........................
----------------------------------------------------------------------
Ran 26 tests in 0.382s

OK
```
I've completed the Contributor License Agreement ("CLA") too.