QueryPerformanceCounter实现Windows微秒级延时

windows的Sleep函数，睡眠线程指定毫秒数，可以用来做毫秒延时。

对于微秒延时，没有一个现成的函数，但是可以通过

QueryPerformanceFrequency

QueryPerformanceCounter

来间接实现。原理就是用循环查询的方式不断调用QueryPerformanceCounter（在Winbase.h中）

LARGE_INTEGER freq;LARGE_INTEGER start, end;QueryPerformanceFrequency(&freq);unsigned int us = 100000;LONGLONG count = (us * freq.QuadPart) / (1000 * 1000);QueryPerformanceCounter(&start);count = count + startQuadPart ;do{   QueryPerformanceCounter(&end);}while(end.QuadPart< count);printf("us %u, elaps %u ms\r\n", us, tpend-tpstart);