Add hopf rule and self-loop removal rules for multigraph

[RazinShaikh]

This is automatic for simple graph but needs to be new rewrite rules for multigraphs

[boldar99]

Should the implementation also apply to these cases?

My idea would be to implement two different functions, one to remove specific edges and another to remove all possible parallel edges between two vertices.

Here, for example, on the top diagram, two edges are selected and removed while on the bottom one, every possible parallel edge is removed as the vertices are selected.

Does this sound good to you?

[RazinShaikh]

It should also take care of the hadamard edges case. I agree that we should have two functions like you mentioned.

[RazinShaikh]

@jvdwetering added these rules in https://github.com/zxcalc/pyzx/commit/904a01c8d7b1bd850f5b494b938b0d337174f86c and https://github.com/zxcalc/pyzx/commit/819421d4ea8267c2edd121e7df269a2a1557759e