implement URDNA2015

[rwst]

A quick skim of code/issues didn't turn up anything. Please implement the RDF Dataset Normalization Algorithm. See also https://github.com/digitalbazaar/rdf-canonize.

[nicholascar]

Looks useful @rwst, are you proposing to implement this yourself? If you need this algorithm for any purpose, please do so and we will review.

[rwst]

I'm tempted, but not right now.