annotate-triples-with-slot-keys option

[luigi-asprino]

This option annotate slot triples with their keys. It is useful when triplifying arrays/lists to express the slot key explicitly so as to: avoid its extraction with the fx:cardinal(?p).
It is necessary when using use-rdfs-member and there is the need to keep the integer key where the element comes from as discussed in #377.

[luigi-asprino]

Maybe better use plural