No graphical interface.

When in graphics mode, the command line interface is very limited. eg. don't
use commands longer than 80 characters. Error messages are even more terse
than usual.

menu() has been minimally fixed for use with demo.ap
eraseing screen with plt(-3) returns to text mode. To give some more
control, plt(-4) clears the graphics text and plt(-5) clears the screen
without returning to text mode.

CtrlC is turned off. Use CtrlBrk.

Hasn't been significantly tested --- not even all the examples have been
run with it.