Some fixes implemented by Zotero developers

Zotero has been using the Tabulator RDF library for a while, and it has accumulated a few tweaks and fixes over the years.

These were implemented on the tabulator RDF library before it moved to git (v 0.8) and that's the lib we use now. Though I still think that all of these are relevant (but maybe I've overlooked something).

For some of these tweaks (esp. the serialization) it might be a good idea to introduce some flags so users can manipulate the output. Let me know what you think. I don't mind tweaking this some more.