Game CD structure

Recognized files
From table in System ROM dumps:
 * IPL file (no type)
 * PRG files (type 0)
 * FIX files (type 1)
 * SPR files (type 2)
 * Z80 files (type 3)
 * PCM files (type 4)
 * PAT files (type 5)
 * TXT files (no type)
 * OBJ files (type 7)
 * A** files, (type 8) ?
 * SYS files (type ?)
 * others ?