FastDFS 追加文件

《1》创建追加类型的文件到FastDFS

storage_upload_appender_by_filename | storage_upload_appender_by_filebuff | storage_upload_appender_by_callback

返回group_name remote_name

《2》向文件追加内容

storage_append_by_filename() | storage_append_by_filebuff() | torage_append_by_callback()