Try using versioneer.

See https://github.com/warner/python-versioneer.

Open questions:
 - [x] Python 3 - supported by versioneer.
 - [ ] [PEP 440](https://www.python.org/dev/peps/pep-0440/) compliant versions - see warner/python-versioneer#9
 - [x] PEP 8 compliant `_version.py` - see warner/python-versioneer#56
It doesn't install it - it's just part of the source distribution. It's needed by setup.py.