Feature request: batch upload/download files

It would be awesome if there were a way to upload and download files in batches - having a method that wouldn't involve connection setup + teardown per file upload/download.

This would be super helpful for projects like [git-remote-dropbox](https://git.io/dropbox) that transfer lots of small objects. (currently, the bottleneck is with having lots of connections and round trips to the Dropbox servers)