Add setup script.

... along with some other files to make it into a proper Python package:

- Add GPL license: murasyp uses pycddlib, so this is a reasonable (only?) choice
- Extensive README, using text from about.rst.
- Set a valid version according to http://www.python.org/dev/peps/pep-0440/
- Add setup script.
- Add requirements.
- Add manifest for source distribution.
- Fix a warning in Sphinx build.