On convergence stopping criterion

[N-Wouda]

In this repository, I saw a stopping criterion that runs until the percentage difference between a new best solution and the old best solution is lower than some threshold. They called it an "on convergence" stopping criterion.

It might be difficult to have this stand on its own, but could perhaps be combined with other stopping criteria. The repository I link to do that as well. So then we would also have to think a bit about how to compose different stopping criteria in a straightforward manner. A simple container class that implements the StoppingCriterion interface should suffice, but we might want to show in an example how to do that.