Instances for testing

Issue #105 has demonstrated that we need better testing of the algorithms.

One approach is to hand-craft tests. But that's pretty slow and limiting.

It'd be better if we could have a set of instances in a file format with a corresponding set of efficient solutions that we could check against.

Here's a library of instances: https://github.com/vOptSolver/vOptLib

It doesn't use a standardized file format, and it doesn't have solutions. But we could translate everything into JuMP and then into `.mof.json` (https://jump.dev/MathOptFormat), and then compare the various algorithms against each other.

The output would be: a standardized set of instances and a set of solutions :smile: which seems like a useful thing for the community.

I'm very open to discussions for ideas on this...