N-Triples whitespace handling according to new erratum

[wouterbeek]

The official list with errata for RDF 1.1 specifications (https://www.w3.org/2001/sw/wiki/RDF1.1_Errata) has recently been extended with a better version of the N-Triples 1.1 grammar: https://lists.w3.org/Archives/Public/public-rdf-comments/2017Jun/0000.html This version makes the occurrence of whitespace explicit.

It's probably best to wait a bit before implementing this in Semweb until the implications for N-Quads, Turtle, and TriG are clear.