ENH: Switch Tox for Nox

[andersbogsnes]

Is your feature request related to a problem? Please describe.
We have been using Tox for a while and are happy with it. Nox does seem like a superior option, being a Python script allows for IDE autocompletion, branching logic and other advantages in having it as a python script

Describe the solution you'd like
Replace tox.ini with a noxfile

Describe alternatives you've considered
Invoke is also an option, but is more low-level. Makefiles are not supported on Windows as easily