Initialize the parser with the given command rules.

def init(self, rules):
        """Initialize the parser with the given command rules."""
        # Initialize the option parser
        for dest in rules.keys():
            rule = rules[dest]

            # Assign defaults ourselves here, instead of in the option parser
            # itself in order to allow for multiple calls to parse (dont want
            # subsequent calls to override previous values with default vals).
            if 'default' in rule:
                self.result['kwargs'][dest] = rule['default']

            flags = rule['flags']
            kwargs = { 'action': rule.get('action', "store") }
            # NOTE: Don't provision the parser with defaults here, per above.
            for key in ['callback', 'help', 'metavar', 'type']:
                if key in rule: kwargs[key] = rule[key]
            self.add_option(*flags, dest=dest, **kwargs)

            # Remember the dest vars that we see, so that we can merge results
            self.dests.add(dest)