(MESS) a7800.c progress:  [Fabio Priuli]
- Rewritten cart emulation to use slot devices
- Removed POKEY chip from the main unit since it was inside
  the carts (of course it gets enabled when you launch a game
  who contained it in its cart)
- Added support for the High Score cart as a passthru cart: when 
  you mount hiscore, a -cart2 switch will become available to mount
  the game you want to play
- Properly implemented XBoarD and XM expansions as
  passthru carts as well, so that new syntax to run dkxm.a78 is
  "mess a7800 -cart xm -cart2 path\to\games\dkxm.a78"
  High Score support for XM shall work as well.
- Big clean up of the driver, simplifying memory map, removing
  writes to ROM, etc.


Out of whatsnew: In conclusion, a7800.c has been brought into the new millennium ;-)