实现AVL树的基本操作。定义了AVL树、结点元素。程序开始时，调用MakeEmpty()函数　　将AVL树初始化，然后调用MainMenue()函数进入菜单选择项，根据输入的选择　　项判断调用相应的程序，实现相应的逻辑功能。-Implement the basic operation of AVL tree. AVL tree is defined, node elements. Beginning of the program, call MakeEmpty () function to initialize AVL tree, and then call MainMenue () function to access the menu selection, the selection according to the input call to determine the appropriate procedures to achieve the appropriate logic function.