router.go
func (r *Router) Group(pattern string, group func(*Router)) {
	c := r.pattern(pattern)
	group(r.clone(c))
}
func (r *Router) Group(pattern string, group func(*Router)) {
	c := r.pattern(pattern)
	group(r.clone(c))
}
// Group calls the specified function with the subrouter for the given pattern