Msise00

Auto-requests past, present, future files for Ap and F10.7 via [gridaurora](https://github.com/scivision/gridaurora) ≥ 1.3.4

Made time, altitude mandatory inputs from command line

allows soft skipping of tests rather than long lists of prereqs for various use cases (plotting instead of file writing)

Update command line API to be less confusing and more robust

Update plotting to handle more cases

CI test numerous plotting/command line cases.

Pep8, mypy, prepare for validation

Using powerful, thin, fast xarray.Dataset for easy access to each of the 4-D data variables output by MSIS (time, altitude, lat, lon).