threadpool 一个C实现的线程池

特征* A thread pool implementation by C language * It is very simply to use thread pool, just need to include threadpool.h in your code * Start all threads on creation of the thread pool * Adding task can be in blocking way or noblocking way * Destory thread pool can be in wait_for_active_tasks way or immediately way未来的工作* Change dynamicly the size of thread pool * Policy-based thread pool