Initial suggestion for extension implmentation.

the `Execute` event allows extensions to register additional command line methods/options.  For instance, the `mkdocs_autodoc` registers the `autodoc-generate` method:

    from mkdocs import events

    def main(event):
         if event.cmd == 'autodoc-generate':
             return True # consumed this event
         else:
             return False # let another event process    

    def includeme(config):
         events.register_callback(events.Execute, main)
         events.Execute.commands.add('autodoc-generate')