Changes to MOS 1.23
-------------------
* All code assumes 32K main memory, never tests OSBYTE 254 for 16K, no "16K" message.
* Reset memory wipe simply wipes from &0400 to &7FFF, setting OSBYTE 254 to &80.
* OSFILE/*OPT1,2/*RUN bugs fixed in CFS/RFS.
* OSFILE fills full control block on return, attributes returned holding RFS link
  address.
* Added *X command, writes to Tube I/O at &FEE8 then hangs, hardware would react
  to this and do something, such as change hardware Tube configuration. This is
  the same command as in the Master MOS.
* *HELP and OSBYTE 0,0 reports OS 1.23
* POINT() does not corrupt the last graphics position by preserving it over the
  call. This means that Plot Triangle will work with POINT between the PLOT calls.

Optimisation:
* Some VDU code moved to allow optimisation and some shared code.
* Some STA xx/LDA xx replaced with PHA/PLA
* Some superflous code removed
 - STY &DC:LDY &DC removed LDY &DC
 - a superflous LDA #" " removed
* Multiple STX &DB:JSR xxxx moved the STX into the subroutine
* Multiple JSR xxxx:LDA #xx:BIT &D0 moved to the test to the end of the subroutine