Since they're determined by the order of sprites in a .BFT file,
they're best auto-generated by an enum as much as possible.
Part of P0074, funded by Myles.
Since a few annoying alignment bytes suggested more translation units
than previously expected, using many small headers has proved to be
better than one big shared TH04/TH05 header file. Or should we *really*
pepper the code with lots of `#pragma codestring`? 😛
And in case we have multiple translation units which all #include the
same set of headers, we'll just go with situational shared headers,
using a common prefix.
Part of P0062, funded by Touhou Patch Center.
nmlgc