从创建Xcode项目的第一集开始，直到第八集让小蛇爬行起来。将来要增加蛇吃果果长大。
还有最后三集请看下面的链接。
金拇指课堂 Golden Thumb Classroom
Snake Game | Draw grid in Xcode
Snake Game | Print empty board
Snake Game | Print board with labels
Snake Game | Refactor snake moving functions and unit test them with XCTAssertEqual
Snake Game | Add 4 buttons to move the snake
Snake Game | Show a static fruit
