consider Extra SHACL features

[VladimirAlexiev]

@HolgerKnublauch
Extra SHACL Features lists some additional features:

• Target Shape,
• Several that come from Allotrope's SHACLC.xtext (links are to a graphical representation of that grammar)

I compared SHACLC.xtext features to SHACL Advanced and listed in the prev section Extra SHACL-C Syntax Features those that map to SHACL Advanced , i.e. are mere grammar and not SHACL additions.

The features are listed below, and IMHO most of them hark back to SPIN:

• Target Shapes
• Shape Libraries
• Imports (how is this different from owl:imports?)
• Parameter declarations.
  Such are present in the SHACL vocabulary https://github.com/w3c/data-shapes/blob/gh-pages/shacl/shacl.ttl#L372 but maybe not the spec?
• Explicit SPARQL syntax. IMHO this is the most contentious feature: should we bring back explicit RDF-based SPARQL syntax? #75