Return an anchor :class:`Html` element with the `href` attribute
        set to the url of this :class:`Router`.

def link(self, *args, **urlargs):
        '''Return an anchor :class:`Html` element with the `href` attribute
        set to the url of this :class:`Router`.'''
        if len(args) > 1:
            raise ValueError
        url = self.route.url(**urlargs)
        if len(args) == 1:
            text = args[0]
        else:
            text = url
        return Html('a', text, href=url)