Upload a whole (tree of) folders

[betatim]

osf upload only works with single files.

Add support to allow the user to upload a folder and its contents or even a whole tree of folders.

[benlindsay]

This feature in my mind would add a huge amount of usability to this cli. My personal use case for this is that I have lots of small files in multilevel subdirectories in a project and I'd want to upload them all at the same time. I am very excited for this feature to be implemented.