This is based on a decorator class, ApplicableMethod, that exposes
methods on objects to direct invocation from the command line.

It uses argparse + subcommands (+ a default subcommand of 'interactive'
to preserve old behavior).

The decorator class methods create argparse subparsers based on
the decorator args for each decorated function.  Kinda cool.  Didn't
end up working as slick as I would have liked, due to decorator
limitations.  But still, useful... and eliminates tons of boilerplate.