Recursive DFS implementations

[ethan-keller]

Hi dagrejs team,

Thank you for the nice graph layout. I know this repository is deprecated, but this issue seemed reasonable to declare since many users might run into this problem.

Many files (e.g., lib\rank\feasible-tree.js, lib\rank\network-simplex.js, lib\rank\util.js) in dagre contain DFS implementations. To the best of my knowledge they are all implemented in recursive fashion.

While recursiveness comes with easier readability and less code, it also comes with limitations. One of them being the limited stack size on a machine.

While using dagre with big graphs (3000+ nodes), I ran into max call stack size errors originating from these recursive DFS functions.

It would be a good idea to rewrite the recursive DFS functions to iterative DFS functions.
This way dagre users can use the dagre layout for their big graphs.