* [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 )

fix issue: Performance problem in zTree init with 1k nodes  when you add exhide.js (Thanks:  https://github.com/sarxos)

fixed issue: if don't use 'exedit' package, the removeNode() method will can't trigger the 'beforeRemove' and 'onRemove' callback.

fixed issue:  if the count of drag nodes is more than maxShowNodeNum, will change some node's  selected state.

fixed issue: The setting's data is wrong which in zTree's method.  Example: checkNode and updateNode...
这个 bug 会导致 设置为 radio 且 radioType=‘all’ 时，checkNode、updateNode方法出现异常