Move files into a proper module.

Seems like structprop wasn't always importable after the changes in https://github.com/edgeware/structprop/pull/5 (most like due to the `py_modules` &rarr; `scripts` change) . This change merely moves the code into a proper Python module.

It's now possible to run `python setup.py test` to run the test suite, or `make test`.

I'm unsure if this requires a bump in version to be able to be uploaded to PyPi or if we can just replace the current one.