Use this NASA image to explain parallel routing order

[jameshalgren]

Suggestion: Incorporate the following animation into the documentation for t-route (be sure to click on the link... the still image doesn't quite do it...).

The animation, produced by NASA in the public domain, shows the concept of the depth-ordered just-in-time parallelization scheme in T-Route. (See jit and jit-clustered for instance here or here.)

https://en.wikipedia.org/wiki/File:The_Rivers_of_the_Mississippi_Watershed.webm