Continue Bessel refactor or switch to inverse incomplete gamma?

So I have ADD. I was working on a refactorization of Bessel whe I started this latest push to clean up the codebase and get it to build in CI. During the cleanup I had to shut down several interrupted projects - one of which was inverse incomplete gamma which has a good answer in the Gil, Segura, and Temme book[1] which I also found their code for. So I see something shiny...

I think I'm going to be responsible and go back and finish the Bessel function refactorization. I was pulling apart these monolithic multi-method functions into separate series and continued fraction functions. I'm well on my way to unifying the treatment of regular and modified bessel functions, and even having these work for complex numbers. We'll see how those latter work out.

Then I'll tackle inverse incomplete gamma.

1. Numerical Methods for Special Functions, Amparo Gil, javier Segura, Nico M. Temme, SIAM 2007.