generate VoID descriptions based on data in an RDF model

 Resource Description Framework (RDF) is a standard model for data
 interchange on the Web.
 .
 VoID is an RDF Schema vocabulary for expressing metadata about RDF
 datasets, intended as a bridge between the publishers and users of RDF
 data. More info at <http://www.w3.org/TR/void/>.
 .
 RDF::Generator::Void takes a RDF::Trine::Model object as input to the
 constructor, and based on the data in that model as well as data
 supplied by the user, it creates a new model with a VoID description of
 the data in the model.