Mermaid visualization

[slwu89]

It seems possible to use the graph keyword (which may just be an alias for flowchart, I can't find any docs on graph) to make a visualization which would be useful for petri net-like structures. Example here. If it handles moderately-sized nets well, I'll consider implementing this when I familiarize myself with the code.

[thevolatilebit]

Let's consider automated visualizations for the refactor.

[slwu89]

I agree. If we stick with Catlab we can use Graphviz, if we use AlgAgents or something else, there should be better solutions than Mermaid.