Ooo, just had a great idea for how to make 3d graph layout easier for flowchart-like constructs.

Basically, what if you use a regular format like graphviz for your usual 2d layout stuff. But then if you place something in a subgraph it goes on a different `z` layer. Such that you can have a bunch of layers but can still have that flowchart arrangement. E.g. you could link up and down between two layers and the nodes would be placed close together.