mux.go
func (mx *Mux) Handle(pattern string, handler http.Handler) {
	mx.handle(mALL, pattern, handler)
}
func (mx *Mux) Handle(pattern string, handler http.Handler) {
	mx.handle(mALL, pattern, handler)
}
// Handle adds the route `pattern` that matches any http method to
// execute the `handler` http.Handler.