Feature request: hypergeometric functions

[YeungOnion]

Over in statrs crate (statrs-dev/statrs) there's some push for features that would absolutely need some special functions. We could include them in our crate, but there's some duplication already, see the functions module.

I prefer to have some separation here because if someone else needs a special function like hypergeometric, I wouldn't assume they'll need distribution functions for various distribution families.

I plan on starting with this myself but some help would be greatly appreciated especially in the sense of I don't know enough about licensing to reference other implementations confidently and I believe that I will be relying strongly on math references like Abramowitz and Stegun along with whatever else I find.

I'm hoping the minimum response I get is if you don't want this in the crate, I'm unsure if the maintenance status.

[IvanUkhov]

Hello, yes, contribution is very much welcome. I will be happy to review and give feedback.