Mostly centered around the HUD, popup, overlay, boss, and player shot
functions we're about to reference in the upcoming decompilations.
Part of P0186, funded by [Anonymous] and Blue Bolt.
Adding op/, main/, and end/ directories does nicely cover a great
majority of the "not really further classifiable slices" implied in
d56bd45.
Part of P0086, funded by [Anonymous] and Blue Bolt.