beginning to write program to automate hw collection and grading

Implementing #17. This doesn't work now on the computer that I'm using, but I wanted to throw it out here while I work on it. Not currently happy with the class structure. Was experimenting with multithreading just for kicks ;)

The basic idea is given a set of Github usernames we download the homework assignments, run `pep8` and `pyflakes` on them, and record the results. I'm a little hesitant to automate anything that would actually run people's code- that seems dangerous.

Feedback welcome.