一个Ftp传输类，有进度条，通过回调设置进度条-Ftp transfer of a class, there is a progress bar, progress bar by setting a callback

C#封装的FTP上传与下载、支持同步操作、一步操作、进度条显示等功能。(C# package FTP upload and download, support synchronization operation, a step-by-step operation, progress bar display and other functions.)