Here's a brief description of the Multi-Botticelli picture format (feel free to clean it up)
- Filenames are prefixed with "m.", e.g. "m.drawing"
- Files are saved from $7800
- Layout: It's the standard Plus/4 image layout. Color map.......$7800-$7BE7 ($03E8 bytes, padded to $0400 bytes) Luminance map...$7C00-$7FE7 ($03E8 bytes, padded to $0400 bytes) Bitmap..........$8000-$9F40 ($1F40 bytes)
- Signature: the last 6 bytes of the color map (in other words, at $7BFA): "MULT" (FF16 color byte) (FF15 color byte) The FF16 and FF15 color bytes are "nibble-reversed": e.g. $71 value will be stored as $17.
