Provide option to include or ignore owl:Thing

[caufieldjh]

Assuming that input entities include owl:Thing as a universal root, we generally aren't interested in including it in IC calculations since it won't make any contribution to that value (it's a root, so it should have an IC of zero).
But it isn't really semsimian's job to make that kind of assumption, so let's provide an option to exclude it or not.
This could conceivably apply to whatever the overall root of the input is if it isn't owl:Thing - though that may depend on having the root identified beforehand.

[justaddcoffee]

I'd vote that we just get rid of any logic in rust that specifically excludes anything, including owl:thing

That is, it's up to the user to provide the ontology, and they can exclude any terms they want beforehand