Add Incomplete Beta Function ratios Ix(a,b) and Iy(a,b)

[Sumegh-git]

This is the initial code for computing the Incomplete Beta function Ix and Iy and returns a tuple similar to gamma_inc.
This is based on the Didonato Paper as referred inside the code docstring for function beta_inc .
Tests will be added soon.

Although I manually performed a few random tests with SciPy and they seem to be working fine.
Also will need to refactor the code to remove the @gotos.
cc @simonbyrne

[simonbyrne]

A nice start!

[giordano]

@Sumegh-git out of curiosity: do you run tests locally before pushing? Pushing a revision that you know is broken spawns 30+ CI jobs that are ineluctably going to fail (in addition to alerting every 10 minutes all people watching the repository) 😉

[Sumegh-git]

@giordano sorry for that. Usually I do, but these were minor tests and I thought they would pass surely.
So I didn't crosscheck locally. But it had some stupid bugs I left while writing the tests. Now it's fixed though.
Would take care not to do this again.

[simonbyrne]

I've flagged a few such changes. See how you go with these and the rest.

[Sumegh-git]

@simonbyrne made the changes as reviewed. Looking for more similar changes if any.

[simonbyrne]

here's a few more suggestions. The beta_inc function is pretty complicated, so will probably take a few passes over it to clear up the control flow.

[simonbyrne]

Also, get rid of the remaining print statments, and SpecialFunctions. prefixes.

[Sumegh-git]

Anything more @simonbyrne ?

[Sumegh-git]

Done @simonbyrne .