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.
… which allows a split into first rendering the top part of every
pellet, then the bottom part. This way, the game only needs two
grcg_setcolor() calls for any number of pellets.
Part of P0085, funded by -Tom-.