This fixes Rance VI which passes SACT2.SP_SaveCG and
SACT2.SP_SetCGFromFile absolute paths like
`system.GetSaveFolderName() + "\\" + "ScreenA.qnt"`.
Also, now savedir_path() uses unix_path() rather than sjis2utf().
Implement a new interface for managing archives. This is mainly to
support loading afa archives alongside ald archives.
Also included here is some code for creating an index for afa CG
archives (the numbers used to reference CGs in afa archives correspond
to the file name, not the position in the archive).
SDL_mixer reads loop information from WAV files if you use the Mix_Music
interface, but NOT the Mix_Chunk interface. So bgm now uses the
Mix_Music interface to get proper looping.
There's also some code here for reading bgi files (taken from xsystem35)
but it's not actually used. There doesn't seem to be a simple way to set
up custom loops with SDL_mixer.
Nunuhara Cabbage