chore: update setup and modernize a bit

[henryiii]

See #58. This is the "deluxe" package mentioned there. You could do a smaller set of changes, including just adding wheel to your environment and python setup.py bdist_wheel —universal. This includes:

• Add setup.cfg to always make a universal wheel (Python 2 + 3)
• Add pyproject.toml to support PEP 517 builds
• Update docs on how to build using PyPA build (still can build classically as well, of course)
• Update setup.py for best practices (including missing python_requires, and proper environment markers for install_requires)
• Replace nose (abandoned since 2015) with pytest (which can run nose tests)
• Minor fix for Python 3 incompatible syntax

[idank]

Sorry for the delay on this, appreciate the contribution! And thanks for reviewing @hugovk.