add flag for produce generalized RDF
Eliminate blank node predicates by default

TODO: Support Options.produceGeneralizedRdf
Support Options.produceGeneralizedRdf
Allow writing of Generalized RDF where predicates can be blank nodes

NQuads parser however does not parse the results of this writing
properly support NQuads printing of predicate blank nodes with spacing
Update tests to Candidate Recommendation

Tests are based on:

https://github.com/json-ld/json-ld.org/commit/6636a82f31131f5429699f1c6a61c1f15221a950
update the test report for the updated testsuite