Use case & requirements document

Hi all ... I've now converted the document skeleton that I documented on the wiki<https://www.w3.org/2013/csvw/wiki/Use_document_outline> into a "proper" W3C document in github ... you can see the document here http://w3c.github.io/csvw/use-cases-and-requirements/. For now, it's only the document outline; I'll be adding stuff across as the week progresses.

Regards, Jeremy