Add auto git-describe version for Python packag...

Add automatic Python package versioning using `git-describe` through the
`version.py` module from [here][1].

A Python package source distribution can be built using the following
command:

    python setup.py sdist

__NB__ The version strings generated by `version.getVersion()` conform
to [PEP386][2].

[1]: https://gist.github.com/mina86/8782771
[2]: http://www.python.org/dev/peps/pep-0386
Add requirements files.
Remove old build scripts, only build docs.
Add install dependencies in `setup.py`.