Python 3 support?

[jayvdb]

Year 2020 has landed ;-)

[jayvdb]

I've done some testing on Python 3, and it looks good so far.

Some test cases and CI would be helpful.

Also, it would be great to see this published on PyPI, where setup.py/pyproject.toml can advertise the Python version support. https://pypi.org/project/ReDoS/ is available ;-) Get it while you can.