return an empty collection, not null
ROSRSException accepts error details.
Fix a bug when creating annotations.
Remove the single-target annotation constructor.
Add isLoaded() to the Annotable interface.
Get property values using a Jena property.
Fix the resource annotation MIME type.
Add author stub.
Return Person, not creators.
Return an empty list for resource without folders if RO not loaded.
Allow to make annotations with RDF nodes.
Always create a new HashSet
Throw exception when creating resource fails.
Remove creator classes.
Annotating resources uses 1 HTTP request.