failing test for TSV result parsing
fix parsing empty bindings in tsv result
Merge pull request #390 from gweis/master

TSV Results parse skips empty bindings in result
Remove "=" graph naming operator from TriG serialization

This was allowed in earlier TriG drafts, but was since removed and is
not allowed by the final W3C Recommendation.
Merge branch 'master' of https://github.com/RDFLib/rdflib into hexstring-bytes