Many thanks to KirbyComment and Colin Douglas Howell for documenting
their research into rank on Touhou Wiki. Just like in TH01, rank also
only affects bullet speed in this game, but let's use the `playperf`
naming scheme from TH04 and TH05 to make it less confusing – at least
until we exactly know the unit of this variable.
Part of P0279, funded by Yanga and Blue Bolt.
The stage bonus functions require the stage-specific ones, which are
updated next to the total ones, which are required by the skill
calculation that we need to explain what we just saw in the verdict
screen… What a coincidence! (Yes, this actually wasn't planned.)
Part of P0279, funded by Yanga and Blue Bolt.
All of these are scalar values with at most a dependency on
`platform.h`. Since these item-related values are mainly read by
score/skill calculation code, it makes sense to declare them in a
dedicated header along with the upcoming metrics.
Part of P0279, funded by Yanga and Blue Bolt.
nmlgc