Radical

Implement JSON-LD writing for Jena :
    a no-brainer

￼Added some documentation for Generic Parameters, with @tparam :
    it is actually pasted in 3 files; maybe do that only in RDFStore.scala ?
I thought that the genric parameter to  makeRDFWriter would do the job.

It's hard to follow all the indirections in Jena.
What I saw for now is that in JenaReadersWriters we have :+1: 
 
   public static class RDFWriterRIOT_JSONLD        extends RDFWriterRIOT   { public RDFWriterRIOT_JSONLD()         { super("JSON-LD") ; } }
    public static class RDFWriterRIOT_JSONLDAlt     extends RDFWriterRIOT   { public RDFWriterRIOT_JSONLDAlt()      { super("JSONLD") ; } }
    
    public static class RDFWriterRIOT_RDFJSON       extends RDFWriterRIOT   { public RDFWriterRIOT_RDFJSON()        { super("RDF/JSON") ; } }