@classmethod
def prepare(cls, parser):
    """
        Called to prepare the extension.  The extension is prepared during
        argument parser preparation.  An extension implementing this
        method is able to add command line arguments specific for that
        extension.  Note that this is a class method; the extension
        will not be instantiated prior to calling this method, nor
        should this method attempt to initialize the extension.

        :param parser: The argument parser, an instance of
                       ``argparse.ArgumentParser``.
        """
    pass
