to add special key support, the following must be done:

1.  add routine to analyze scan code from Bconin(), increment all
    special keys to invalid ascii values, just over the valid value range.
    This will entail going through the manipulations MS-DOS has to.
    See getch.c for the basic procedure.
2.  increase NCHARS (in "sysdep.h") by 60 (40 Fkeys + additional 20
    speckeys and alt & control combinations).

#ifdef MiNT
#define SPECKY 1
#ifdef NCHARS
#undef NCHARS
#endif /* NCHARS */
#define NCHARS 0274
#endif /* MiNT */

3.  rework the bindings tables in keys.txt to handle the additional
    60 bindings.
