该源码实现对二叉树的线索化，先序、中序、后序线索化二叉树，并提供了先序、中序、后序遍历线索二叉树的功能。-The source tree to achieve the clues, the first order, in sequence, after the sequence of binary tree clues and to provide a first order, in sequence, after clues tree traversal function.