Extend collection validation features

[jeswr]

In #403 we implement support for #391 (sh:memberShape). As discussed in #403 (comment) we may wish to support some other constraints on collections - including:

• sh:minCollectionLength and sh:maxCollectionLength (I think we SHOULD support this)
• sh:uniqCollection to check that all elements in the list are unique (I think we SHOULD support this)
• sh:memberCompare which operates similarly to property pair constraints by comparing adjacent elements; e.g. to enforce numeric ordering. (I am on the fence about supporting this)

I would like to land #403 before implementing these if we choose to proceed.

[HolgerKnublauch]

Yes to the first three, but I would call them sh:minListLength, sh:maxListLength and sh:uniqueMembers (boolean). The term "collection" is easy to misunderstand, e.g. for Java people where Collection is a super interface for List.

[afs]

+1 to "list" -- RDF has rdf:List in the "RDF Collection vocabulary".