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 ?
Can you please remove the `org.w3.banana.io.`? And add a space after the commas? (same thing in all the other places :-)