use puml "hide" options

Please use
```
hide empty members
hide circle
```
to make the diagrams a bit lighter.

I have a similar tool https://github.com/VladimirAlexiev/rdf2rml/blob/master/doc/rdfpuml.md
that focuses on displaying instances,
but can also display ontologies, eg https://github.com/VladimirAlexiev/rdf2rml/tree/master/test/blank-types#examples