//撤销悔棋，恢复到下一个备忘录
static void Redo(Chessman chessman)
{
Console.WriteLine("******撤销悔棋******");
index++;
chessman.Restore(mementoCaretaker.GetMemento(index));
chessman.Show();
}
//下棋，同时保存备忘录
static void Play(Chessman chessman)
{
mementoCaretaker.AddMemento(chessman.Save());
index++;
chessman.Show();
}