Create Revision from JSON

- Create a document revision with attachments from a Map of <String,Objects>
- Create SavedHttpAttachment class


Only one question, If a URISyntaxException is thrown, should this be propagated back to the user, or should an IllegalArgumentException or IOException should be thrown instead?
i) indenting
ii) it might be better to check for data than stub. It's possible to have stub = false and data not present. This is the case for mime/multipart, although I concede it would be odd to have a document which came from this source.