is_comparative() and is_superlative() missing

[lsmith77]

are these functions intentionally missing? or would you accept a PR adding these?

[tomaarsen]

They're not intentionally missing. I started work on these back in the day, but I believe I couldn't get good enough performance.
Another factor is that the project that inspired this one, https://metacpan.org/pod/Lingua::EN::Inflexion by Damian Conway, does not include converting to comparative and superlative. Those are features I added myself, and so I did not have a premade file of conversion rules and exceptions that I could base my work off, like I had for nouns and verbs.

I'd accept a PR for these, if you're willing to work on it!