need python_requires or something to prevent pip/PyPI from thinking 0.17.0+ works on Python2

[YKdvd]

Version 0.17.0 dropped support for Python 2.7, but there is no "python_requires" in setup_config or anything else that prevents PyPI and/or pip from thinking it is a valid release for Python 2.7, and it will install but of course not work.

I think an appropriate "python_requires" in setup.py, and "yanking" 0.17.0 from PyPI, would do the trick?