code: func NewGroupRouter(r *Router, path string) *GroupRouter {
  	gr := &GroupRouter{}
  	gr.router = r
  	gr.path = strings.TrimRight(path, "/")
  	return gr
  }
docs: // NewGroupRouter return GroupRouter which is a helper
  // to construct a group of endpoints, such example could
  // be API-version or different methods for an endpoint
  // You should always use router.Group instead of using this directly