[Coco] Having fun with hacking HDB-DOS

[Juan Castro]

Now the WIDTH command works and drops you in the PMODE 4 screen if the
argument is 51 or 64. WIDTH 32 takes you back to text mode. Also, all
CoCo 3 tokens are recognized. But, of course, all but WIDTH will give
you an error.

Next up: LOCATE. Then... BUTTON? ERR/ERNO/ERLIN?

ROMs: https://dl.dropboxusercontent.com/u/15643089/16kroms.zip
Source patch: https://dl.dropboxusercontent.com/u/15643089/hdbdos-16krom.patch

Juan