Changes
if compressed:
byte 3,4: size of compressed graphic data
byte 5-n: compressed linear graphic data (ZX0 with special SymbOS -specific header, see below)
</pre>
if compressed:
byte 8,9: size of compressed graphic data
byte 10-n: compressed linear graphic data (ZX0 with special SymbOS -specific header, see below)
</pre>
