function request(method, url) {
  // callback
  if ('function' == typeof url) {
    return new Request('GET', method).end(url);
  }

  // url first
  if (1 == arguments.length) {
    return new Request('GET', method);
  }

  return new Request(method, url);
}
POST `url` with optional `data` and callback `fn(res)`.

@param {String} url
@param {Mixed} data
@param {Function} fn
@return {Request}
@api public