More rendering options added.
Functions for owlthing and owlnothing.

These functions return the owl builtins. Could have made these
vars, but functions are robust against re-evaluation of the
ontology-data-factory.
New predicates: disjoint? and equivalent?

These check for declared disjoint or equivalence.
Added option support into as-subclass macro.

Although there is already an as-disjoint-subclass macro, this approach
does not scale if there is more than one kind of option -- such as covering
for instance. So, the as-subclass macro now supports the :disjoint and :cover
axioms
Added a :pre condition for add-equivalent

This fails silently if a single class is passed, which is not very
consistent with it's name. Adding a pre condition picks this up
nicely.
Tests for new options functionality.