Allow Turtle/TriG as both input and output in the playground

[gkellogg]

Playground serializes to N-Quads, but doesn't provide a way to start with any RDF. This would be quite useful in some contexts. The N3.js package could make this fairly straightforward.

[niklasl]

Although I haven't stabilized the API yet (and could still consider it an experiment), I've also made an RDF parsing tool: LDTR (for Turtle, TriG, RDFa and RDF/XML). It has the interesting property of using a transcribing approach directly into JSON-LD. That means that it preserves the order and general shape of the input quite accurately. It also means that it uses JSON-LD directly, without any intermediate triple representation.

[gkellogg]

Cool, that would be a nice edition. We'll probably still need something like N3.js for N-Quads to Turtle/TriG, unless LDTR handles that too.