Remove the deprecated optparse module and replace it with an similar
implementation using argparse.

Find and fix various problems reported by pylint.

Fixes everything but a single case where the options are either an
E129 warning about having the same indentation as the next line or an
E127 warning about over-indentation - and there doesn't seem to be a
format that satisfies the checker!

Enable command line argument completion for the two directory options
if/when argcomplete is available.

To keep the linter happy, most of the format() calls with f-strings.
This supposedly offers better performance and is more in keeping with
python 3.