Releasing

Because I always forget how to do this for Python modules:

Merge code changes into develop
Use gitflow-pp script to run gitflow-pp.sh release start and specify the appropriate version to be released
Update HISTORY.rst with the version to be released (and release notes, if not already done)
Update setup.py with the version to be released
Run gitflow-pp.sh release finish
Verify that the git branching model looks sane
Run gitflow-pp.sh push

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