Add graph isomorphism computation

[dominikbraun]

Graph isomorphism can be used to determine whether two given graphs are structurally equal, or simply put "the same".

It may look like a trivial check at first glance, but it is one of the hardest problems to solve in graph theory.

There are a couply of algorithms for computing isomorphisms of two graphes, and I don't have a strong opinion on which one of them I would like to see implemented in this library.

• VF2 (VF2 Python implementation)
• Bliss
• Nauty
• CISC

At this time, I would prefer a simpler implementation that works for 80% of use cases and graph sizes over a more complex implementation that covers 99% of possible graphs.