grouprouter.go
func NewGroupRouter(r *Router, path string) *GroupRouter {
	gr := &GroupRouter{}
	gr.router = r
	gr.path = strings.TrimRight(path, "/")
	return gr
}
func NewGroupRouter(r *Router, path string) *GroupRouter {
	gr := &GroupRouter{}
	gr.router = r
	gr.path = strings.TrimRight(path, "/")
	return gr
}
// 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