Tool to weight graph edges by number of routes to the root node(s)

[Notgnoshi]

Take a tree, and weight the edges so that the arterial edges can be drawn thicker.

Should work on non-tree graphs. Requires picking a random root, or specifying node(s) to be root(s).

Input should be TGF with optional node labels, and no edge labels. Output should be TGF with numeric edge labels.

See also https://github.com/jasonwebb/morphogenesis-resources#medial-axis

Related to #52