Switch version handling to use setuptools_scm

[lowell80]

Consider dumping the custom git describe parsing function in setup.py and replace it with setuptools_scm instead. This should save pain long-term and reduce silly code (at the cost of an additional development-time library; which is fairly low.)

pip install setuptools_scm

Use either write_to or write_to_template to create the version.py file (or continue using the existing code if need be.)

May need to add setuptools_scm to the requirements.txt file (or a dev version of that file) and install it for Travis/AppVeyor.

References:

• https://pypi.org/project/setuptools_scm/
• https://github.com/pypa/setuptools_scm/blob/master/setup.py

[lowell80]

Also consider bumpversion as an alternative approach.

https://pypi.org/project/bumpversion/