Consider migrating to docopt-ng for Python 3.12 support

[vinnybod]

https://github.com/docopt/docopt is unmaintained and is not fully compatible with Python 3.12 due to its use of invalid escape sequences.

There is a maintained fork of docopt called docopt-ng that is a drop in replacement.
By migrating to docopt-ng this project is more likely to be compatible with Python 3.12.