Release procedure (version number bumping)

[jonascj]

I just did release 0.9.2 to PyPi and the release procedure is error-prone. Less now than when I release 0.9.0 and 0.9.1, but still error-prone.

At the moment the version number has to be changed in setup.py and sphinxcontrib/images.py manually. release-to-pypi.sh (which does not interact with pypi.org) checks if the two version numbers match and it checks if the lightbox2 submodule is initialized. That is an improvement over the 0.9.0/0.9.1 jumble...

When doing a test upload to test.pypi.org with twine you can only use any given version number for one test, so if you test with version 0.9.2 you can not retest with 0.9.2, but only with 0.9.3 or 0.9.2.pre2. This error-prone, having to change version numbers (to add .preN) to test on test.pypi.org and then have to change them back (and rebuild) before uploading to pypi.org...

Of course it is doable, but I'm open for suggestions to make it less error-prone. Any ideas @t-b ?