Random Hill-Climbing Algorithm for STS Generation

[Joshua Ganschow]

Hello, all. I have an implementation of Stinson's hill-climbing algorithm for generation of Steiner Triple Systems based on the implementation in the book "Combinatorial Algorithms: Generation, Enumeration, and Search" (Link to book). I have a version added into the existing `combinat.designs.bibd` module. Any considerations to make before I open a PR?

Link to my fork: Github