ISSUE-41: Progress

I have updated the spec to the new syntax for property paths. This 
includes the new property sh:path and a proposed syntax for the path 
expressions themselves, see section 2.3.1:

     http://w3c.github.io/data-shapes/shacl/#path-syntax

In the last meeting the following resolution was made:

*RESOLUTION: change PropertyConstraint and InversePropertyConstraint to 
one type of Constraint with either a predicate (which implies arcs-out) 
or a path. The path does not include * or + and cardinalities on the 
resulting node value set are satisfied by combination of cardinalities 
on the steps. Exact syntax (e.g. nested paths, behavior of bnodes) to be 
resolved.*

I suggest two changes to that resolution
1) To mark ISSUE-41 as closed
2) To include * and + operators

Does anyone remember why * and + were excluded? It feels like a very low 
hanging fruit given that SPARQL engines already provide this capability 
and even an implementation "by hand" is not more than a walk-through of 
property values. Given that the * operator is frequently used in tree 
structures and covers many cases that would otherwise need SHACL 
recursion, I would prefer it to be included. The current spec includes 
every path feature from SPARQL 1.1 including inverse, sequence, 
alternative paths, but except NegatedPropertySets (which feel rather 
complex to specify and barely used):

https://www.w3.org/TR/sparql11-query/#pp-language

So my updated proposal would be

PROPOSAL: Close ISSUE-41 using the syntax described in the current spec.

Thanks,
Holger