Convert to unit tests

[garybernhardt]

Maintaining this documentation as a doctest hasn't turned out very well. Some examples aren't illustrative because they don't represent realistic use cases. Everything is fragile because it's all mixed into one environment.

Instead, let's turn them all into standard unittest classes. We'll need to parse the test files to generate the documentation. Comment markers in the test files are probably easier than trying to parse the test methods out directly.