Add an ASCII translation table which can be used with puttext() and mostly

reversed via gettext() for non-ASCII fonts such as Commodore and Atari.

This functionality is enabled via the ciolib_xlat variable.  Setting it to
zero (the default) means no translation is done.  Non-zero translates from
ASCII to the current font.

This functionality is only available to built-in fonts.  No attempt to
allow user-defined or BBS-defined fonts to access this functionality is
planned.  If you want to use custom fonts, use ASCII.