Add proposal to include subset of Hydra into Schema.org
Comment out unnecessary issue marker
Reference Turtle serialization from Core Vocabulary spec

... and remove dead link from schema.org proposal to core.jsonld.

The Turtle serialization is generated on the fly by the RDF Translator at http://rdf-translator.appspot.com/

This was requested by Kingsley Idehen, see: http://lists.w3.org/Archives/Public/public-hydra/2013Nov/0033.html
Merge branch 'master' of github.com:HydraCG/Specifications