希望assetsmanager里面的功能能在jsb中单独使用

[kawais]

如下载文件，保存，解压，md5校验。

[pandamicro]

As for file save, uncompress, md5 verification, they should be features of FileUtils, we have a discussion thread for this topic:

We have send a feature request to Cocos2d-x repo: cocos2d/cocos2d-x#9621

As for download file, it means we should bind Downloader APIs, we will also consider it.

[kawais]

还有删除、创建目录/文件