Shexer

After last release, sheXer could brake when extracting shapes using a property both to point to literals and IRIs. That is fixed in this release.

- Extraction works properly even if there are BNodes as target instances or in the neighborhood of those whenever a non-rdflib parser (TURTLE_ITER, NT) is used. In the rest of cases, BNodes are ignored.
- No <BNode> shape will appear in any constraint. The macro BNode is now properly used.
- The macro NONLITERAL has been introduced to generalize situations in which both BNodes and IRIs play the same role w.r.t some target nodes.
- Bug related to cardinality in OR constraints has been detected and corrected.

Now the messages outputed with the verbose mode are written to std_err, so they are not mixed with resulting schemes being written in std_out