Python: Set up unit test infrastructure

[divergentdave]

This moves test and test vector-related code from if __name__ == "__main__" blocks to separate unit test files, using the unittest framework. This will make CI more manageable as this implementation expands, since unittest does test discovery by default. In the future, we may want to redirect test vector output to a series of files, or conditionally do so based on an environment variable, rather than having the tests just print to standard output. For now, I have just forklifted all the code over, and passed --verbose to unittest to get some extra newlines.

This is stacked on #128.