Closes#43
FBNeo and Kronos expect BIOS archives in core-specific subdirectories
(system/fbneo/, system/kronos/). RetroArch firmware check uses .info
paths which include these prefixes, so files at root show as Missing.
Add archive_prefix field to emulator profiles. The pack code now places
archive copies in the prefixed subdirectory while keeping root copies
for cores that expect them there (e.g. Geolith for neogeo.zip).
trackball BIOS (236-bios.sp1, 236-bios_japan_hack.sp1) for irrmaze,
PCB BIOS (sp-4x.sp1, spj.sp1) for ms5pcb/svcpcb/kf2k3pcb. all carry
BRF_ESS flag in d_neogeo.cpp, verified against source.
