A simple coroutine library for c++, modeling coroutine from lua.

usage:
1. create a schedluer:
   CoroutineScheduler* sched = new CoroutineScheduler(1024);
2. create coroutine:
   int id = sched->CreateCoroutine(func, arg);
3. run coroutine:
   uintptr_t ret = sched->ResumeCoroutine(id);