Setup nox for automating routine package maintenance

[mcflugen]

This pull request sets up nox for automating routine package maintenance task like:

• running the test suite for multiple python versions
• testing the notebooks
• testing the command line interface
• looking for lint (flake8, black, etc.)
• building the docs
• making sure pull request have a news fragment

Since this is pretty much what we had in the Makefile (and a little more) and is platform independent, I've removed the Makefile.

@mdpiper This might be something you would be interested in.

[mdpiper]

@mcflugen This is cool! Maybe also include nox sessions for clean, build and deploy to PyPI?

[mcflugen]

@mcflugen This is cool! Maybe also include nox sessions for clean, build and deploy to PyPI?

@mdpiper Good idea. I've added additional sessions.