[Reduction] #673-680: BERO's Pi loader library

> randomly google "PC-98 ライブラリ"
> 3rd hit: http://www.vector.co.jp/soft/dos/prog/se037608.html
> Oh look, it's the mystery code at the beginning of the TH01 executables!

This library also has dedicated support for transparency, which is used in the
Konngara fight (BOSS8_D*.GRP) and which we couldn't edit during the
development of the static English patches.
But of course, ZUN just had to change the format magic in order to make it
seem unique.