Changes

* The snapshot format doesn't support more than 512K RAM and only supports dk'tronics compatible RAM expansions.* The snapshot format doesn't support additional hardware. A basic CPC464, CPC664, CPC6128 system is assumed.* The snapshot format doesn't support KC Compact or Aleste hardware.* The snapshot doesn't have knowledge of which ROMs are in use. This means it doesn't know which OS, BASIC or AMSDOS ROM, and nothing about expansion roms.It generally assumes a CPC6128/6128Plus system with ram expanded up to 512K.