query specific file type in list method

[Gary.Wang]

A scenario is e.g..
I have 1000 files in one folder, some of them are pictures, some of them are videos and some others.
I just only wanna query all pictures on storage client.Currently, It's inefficient to iterate all files in one folder to find specific file type.

for mcloud library, there is a provided parameter to query the following file type
>> enum class Type {
          All, ///< all kinds of content type
          Image, ///< png, gif, jpg content
          Audio, ///< mp3, ogg, wav content
          Video, ///< mp4, avi, rmvb, mkv content
          Doc, ///< doc, dox content
          Speadsheet, ///< xls, xlsx content
          PPT, ///< ppt content
          Other
      };

I am not sure if any other storage services have similar stuff. But I think it's better to support query for the specific type in list method for efficiency purposes.