stacking bars

[armatures]

After poking around the code a bit, it looks like it might be possible to extend the viewActualBars function to allow for stacked bars instead of clustering them adjacent to one another on the x-axis. Does this make sense to add as an option in the Bars type alias?

Sorry I don't have much context about this project but I'm curious and interested. If that's a sensible API idea I'd happily hack on it a bit.

Thanks, and great work!