Per-game parameters are (tag, value) pairs that follow the same tag
structure than everything else. They're added within a ROM section
with ROM_PARAMETER(tag, value). You look them up through the device
method parameter(tag) which returns the string, or "" if not present.
A *lot* of drivers can benefit from that stuff. It should kill most
game-name keyed tables, and the alternative approach of
bazillon-of-driver-inits.
Possible evolutions, if someone wants to do it:
- output them in -listxml
- push the softlist parameters present in the xml through that
- maybe allow to change/set them through the command line
