Build a ``url`` from ``urlargs`` key-value parameters

def url(self, **urlargs):
        '''Build a ``url`` from ``urlargs`` key-value parameters
        '''
        if self.defaults:
            d = self.defaults.copy()
            d.update(urlargs)
            urlargs = d
        url = '/'.join(self._url_generator(urlargs))
        if not url:
            return '/'
        else:
            url = '/' + url
            return url if self.is_leaf else url + '/'