说明：  4*4矩阵键盘扫描函数,用状态机实现,不用延时以消抖,只需在一个定时10~12ms左右的中断函数里调用,从而节省了单片机时间
(4* 4 matrix keyboard scan function, the state machine to achieve, not delay to eliminate buffeting, only in a regular 10-12ms about the interruption function within the call, thereby saving the time of microcontroller)