Assert() that FORTY command is not too long.
Tolerate missing print (or print->push) command.
Don't return status from forty_print.

This is for simplicity's sake. Instead, forty should
degrade gracefully on invalid input (and possibly write
to a log file.)
Add top function to SS.
Rework FORTY (WIP).

- Properly handle pops of invalid pushes.
- Don't reset the scratch buffer unnecessarily.
- Refactor code.
- Bug fixes.