New BASIC 4.0 (v1.3)

With this BASIC update 4.0, I have mostly added some missing functionality to increase the compatibility with different Commodore computers and the Commander X16. 

New commands include VPOKE and VPEEK for screen access. With these new commands, it is not necessary to remember the correct screen addresses: The screen starts with bank 0 at address 0, so VPOKE 0,0,1 (bank,address,character) will poke an "A" in the top left corner. Additionally, to make it compatible with Commander X16 BASIC programs, VPOKE 1,45056,1 will do the same thing.

Another new command, which only exists for Commander X16 compatibility, is the SCREEN[number] command, although no matter what parameter it gets, it does nothing but clear the screen.

For more compatibility with Commodore BASIC programs, there are now more screen addresses to use with the original POKE and PEEK commands: 1024, 3072, 32768 and 53248 all poke to the top left corner of the screen.

In order to increase compatibility with Plus4 code, there's also a new function JOY([number]), which will always return the value 256.

There are also some other minor improvements in the new BASIC version, like the ability to use hex numbers (e.g. $FF = 255) and being able to combine NEXT commands (e.g. NEXT X,Y). 

Lastly, using the LOAD command to load a BASIC program from a running BASIC program should now behave correctly instead of stopping the execution.

As a proof of concept, I have also updated the ZieBieEmm Gaming App to include the Schlangenwurm X16 code.