贪吃蛇游戏,实现上下左右四个方向的运动,实现运动速度控制,蛇在吃到食物后会长长，吃到一个食物后会长长一个单位,记分功能-Snake Game, realize the four directions of up and down about sports, sports achieve speed control, a snake eating food at long after, food to eat after a long a unit, function points