Support: node data is { name: "Node2", children: [ ] }, zTree will set this node is parent node (isParent = true)

   * [修改] reAsyncChildNodes 方法增加 callback 参数

   * 【增加】treeNode.getIndex 方法，可以快速获取 节点在 子节点中的位置
   * 【增加】treeNode.getPath 方法，可以快速获取 节点的所有父节点

 * 【修改】selectstart 事件未解绑导致的内存泄漏

remove the 'event' parameter in 'onSelected/onUnSelected' callback.  And when you remove the node which be selected, zTree will trigger the 'onUnSelected' callback.

Allow nodes to specify their own icon using an 'icon' property of the 'setting.data.key'  (Thanks  davidsk )