   GSH save file
   same as GST with the following differences

   A GSH savestate should be backward compatible with GST

   Range        Size        Description
   -----------  -----       -----------
   00000-00002  3           "GSH"
   00440-00447  8           Mapper registers
   22478-EOF    variable    Binary data - non portable


   Sega (aka SSF2) Mapper registers
   ----------------------
   00440 : 0xA130F3
   00441 : 0xA130F5
   ...
   00447 : 0xA130FF