Write the right_edge to the binning output.
More work on encoding the fill/stroke distinction and plumbing that
through the pipeline. This is a bit unsatisfying because of the code
duplication; having an extra fill/stroke bool might be better, but I
want to avoid making the structs bigger (this could be solved by
better packing in the struct encoding).
Fills are plumbed through to the last stage. Backdrop is WIP.
As of this point, it mostly renders stroke outlines for tiger. Some
dropouts are because the scan in the elements pass doesn't do lookback
yet, others are probably a bug.
