说明：  实现二叉树链表表示的二叉树： 建立一棵二叉树； 按先序、中序和后序遍历二叉树； 按层次遍历； 求一棵二叉树的高度； 交换一棵二叉树的左右子树； 复制一棵二叉树。
(Realize that the binary tree binary tree list: building a binary tree by the first order, in sequence, and after traversing a binary tree by level traversal seek a binary tree of height exchange of a binary left and right sub-tree tree copy a binary tree.)