Context: #144

often we want to suppress generation of induced slots Class__Slot, e.g.

• in markdown
• in OWL

These are already effectively suppressed in PythonGen, JsonSchemaGen, etc

some projects such as CCDH rely on having separate induced slots in the markdown, since they may be reusing slot names with vastly different semantics. However, in other cases e.g. mixs, we just want to use slot_usage to provide some minimal adornment onto a standard slot. Also when using attributes as a shorthand convenience we don't want to see these.

To satisfy all I would like to make this a switch. I propose the default is expand_slots=False, but this would require us in CCDH to be careful about adding this switch when the new implementing version is released