34404 create rev from json

Allow the creation of CDTDocumentRevisions for use with remote data sources
So, this requires the NSData not only to be JSON, but to be a "CouchDB JSON" document, which isn't documented. 

Might it be better to do this in CDTMutableDocumentRevision object, allowing one to pass in JSON without _id / _rev and then leave it up to the user to modify _id / _rev if needed? Of course, IF _id and _rev are in the JSON, then that should be added to the CDTMutableDocumentRevision before it is returned.

Also, one could get a JSON doc from Couchdb/Cloudant with the meta=true, or revs=true, or revs_info=true (and others: http://docs.couchdb.com/en/latest/api/document/common.html). Passing that JSON doc, which will contain the "_revs" and "_revs_info" keys, into here would fail -- and the error would probably not be very helpful.

Might want to take a look at `TDJSON -isValidJSONObject:(NSDictionary*)` and the TDJSON -JSONObjectWithData, although it's a little obscure as to what it does. Sorry, I don't have time right now to really look at this in particular to see if this is useful for you.