Build a skew normal distribution

https://en.wikipedia.org/wiki/Skew_normal_distribution

In fact, it would be good to look at the R sn utilities - at the API at least - for generalized skewing.
If we could do skew_distribution that would be cool.
We'd want a general tool to shift and shape too. x -> (x - m) / s.

Start by reading the linked Wikipedia description and reviewing the R sn utilities API for generalized skewing. Then inspect this repository's existing C++ random distribution facilities to determine how a skew_distribution interface and the requested shift-and-scale behavior would fit. Done means the design and scope are agreed before implementation begins.

Written by the indexing model from the issue text.