[Versa] Issue 100A proposal, extension functions

[Chimezie Ogbuji]

 > I think we should eliminate vtrav and all other derived Versa
> namespaces, and just use the main Versa namespace.

Okay so if you collapse vtrav with the versa namespace
(http://rdfversa.org/ns/2/0/) you have:

versa:forward - Indicates moving forward through a traversal , where
the order is from subject to object.

versa:inverse - Indicates moving backwards through a traversal , where
the order is from object to subject

versa:transitive - Indicates moving continously along an RDF graph
traversal (calculating a transitive closure of the traversal)..