Use RDF 1.2 rather than RDF 1.1

[Sveino]

RDF 1.2 Concepts and Abstract Syntax is now a Working Draft:
https://www.w3.org/TR/rdf12-concepts/
Rather than going to RDF 1.1 in the first version of support for JSON-LD, we could go straight to RDF 1.2: (https://w3c.github.io/rdf-new/spec/

RDF 1.2-Turle:
https://www.w3.org/TR/rdf12-turtle/