Jena reader writer

RDFReader and RDFWriter implementation for Jena

This registers "JSON-LD" as a language with Jena's model.read() and model.write() - which makes it much easier to do for instanc eJSON->Turtle in one go.


See documentation on https://github.com/stain/jsonld-java/tree/jena-reader-writer/integration/jena

Related issue #51 https://github.com/jsonld-java/jsonld-java/issues/51 with a more longer term solution for RIOT (which I'm not sure if would hook into model.read() / model.write().)