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