code: func (n *Node) Handle(method string, handler interface{}) {
  	if n.GetHandler(method) != nil {
  		panic(fmt.Errorf(`"%s" already defined`, n.getSegments()))
  	}
  	n.handlers[method] = handler
  	n.allow = append(n.allow, method)
  }
docs: // Handle is used to mount a handler with a method name to the node.
  //
  //  t := New()
  //  node := t.Define("/a/b")
  //  node.Handle("GET", handler1)
  //  node.Handle("POST", handler1)
  //