qt实现计时器功能，用到qt的信号与槽机制，能够根据全局变量的变化控制计时器的开始和结束！-Qt realize timer function, use qt signals and slots mechanism, according to the change of global variable control the beginning and end of the timer!

一个精确到微妙的计时器程序。可实现高精度计时。-A precise timer to delicate procedure. Can achieve high-precision timing.