Use built-in test discovery function. Follow the Python coding convention.

First I just want to say thanks for creating the cyber-dojo! It's fantastic.

I think the Python starting point should follow the coding convention [PEP8](http://www.python.org/dev/peps/pep-0008/).

I also think it would be great to use the built-in test discovery function. It will find and run all tests in all files (following the naming convention test*.py).