将含有多层子目录的某个目录下的全部文件，抽取到某个目录下（无子目录）。用多线程实现，一个搜索线程，一个拷贝线程，使用windowsAPI函数-The entire file to a directory containing subdirectories under multi-extracts to a directory (no subdirectories). With multithreading, a search thread, a copy of the thread, use windowsAPI function