Create a --help page that shows available plugins

[Garandor]

Pluginnames are not listed, all options are sorted alphabetically and shown together, this will get overwhelming quickly.

At least show available plugins and group cli options by the plugins that need em

Status quo:

Usage: ./pfcrender [options]
pfcrender

Options:
-h, --help Displays this help.
-v, --version Displays version information.
--it Number LSYS iterations to compute
--rules Comma seperated list of LSYS axiom and rules for
stringsubst