One fewer magic number. And one more deliberate dependency on a
PC-98-specific hardware constant, to further drive home just how
unportable these games are, even once decompilation will be complete.
Part of P0105, funded by Yanga.
Leading to slight complications in TH02's Music Room and shot type
selection menus. Thought about leaving those in C for a while, but I
still think it's worth it for the consistency we get with the VRAM
offset functions. Also, we'll have similar code for the main menus of
later games, and I'll surely won't be using C++ when starting out with
these.
Part of P0105, funded by Yanga.
nmlgc