Work-in-progress / JSON-LD for jena RIOT

[Andy Seaborne <an...@apache.org>]

To test out the integration of other parsers and writers, I wrote the 
adapters needed for JSON-LD using https://github.com/tristan/jsonld-java 
as the JSON-LD engine.

https://github.com/afs/jena-jsonld#readme

Seems to work for reading and writing JSON-LD from Jena with model.read 
and model.write.

Currently, the jsonld-java jar has to be built from source - it's 
dependencies are the Jackson JSON processor (license: AL).

NB depends on Experimental/riot-output for writer integration.

riot-output is ready for integration into RIOT.  As the release seems to 
have been OK, I'll now put RIOT output into trunk.

	Andy