Use external tools for formatting and style

[spco]

We currently roll our own Fortran formatters: tools/fix_style.py and tools/fix_indent.py. Since the main development work on AtChem2, things in the Fortran world have really come on - I suggest we make use of https://github.com/pseewald/fprettify instead. It'll reduce our own estate we need to maintain, and be more robust and better tested.

In a similar vein, we should run https://pypi.org/project/black/ on our Python files - it's very opinionated but that's the point, removing our own preferences.

If you agree (with either), I'd be happy to make a PR. I'd recommend merging #497 first, as it'll undoubtedly change stuff all over the place.

[rs028]

This sounds like a good idea, both for Python and Fortran.