mux.go
func (mx *Mux) Options(pattern string, handlerFn http.HandlerFunc) {
	mx.handle(mOPTIONS, pattern, handlerFn)
}
func (mx *Mux) Options(pattern string, handlerFn http.HandlerFunc) {
	mx.handle(mOPTIONS, pattern, handlerFn)
}
// Options adds the route `pattern` that matches a OPTIONS http method to
// execute the `handlerFn` http.HandlerFunc.