ZXpand+ Support

In real life this add-on for the ZX81 provides 32K of RAM, ZON-X compatible AY sound,
and SD card reading support, controlled through a patched ROM. In EightyOne you can
enable this board from the Hardware dialog by checking the ZXpand+ option.

Files placed in the folder 'ZXpand_SD_Card' are treated as a virtual SD card.

Press Z to get the CAT command in order to list the files on the emulated SD card.
CAT "directory name" will show files within a subdirectory.

The LOAD command is patched so files will be loaded from the virtual SD card rather
than the tape system. On a real ZXpand typing LOAD "" will invoke the tape loader
and allow files to be loaded that way. Under EightyOne emulation however this does
not work due to the way that the emulator handles the ROM patching.

SirMorris
