-Starting to play around with history navigation
-Looks like reading backwards is the bottleneck here; noticeable delay between release and re-render (and it's not because the front-end notebook! function is too slow).

Options:
       - Notebook-specific overrides for fact-base behavior
       - Change fact-base such that load! takes an additional argument to specify whether it'll be running in-memory or on disk. This'll require changes to apply-entry, reverse-entry, load!, and the rewind functions (they need to check in-memory history for relevant fact-bases and hit disk for ones that don't care)

I like the second one, obviously, but I'll think on it for a bit.