文件移动、拷贝的类库 限定大小

　　The purpose of this class is to copy or move the files to a set of directories, so that the total size of all files in each directory does not exceed a given size limit.
　　It can can be quite handy in situations where you need to transfer an huge amount of files, which would be a tedious job to perform manually.
　　This kind of problem is also known as bin packing. Current, this class only solves this problem partially.