Switch to using Unicode input.

Switch to using Unicode input.

I failed to notice that getch() delivers you single bytes in trad
fashion. Switched to get_wch(), which returns either a Python char
(that is, a length-1 str) or an integer containing a curses key code.

Also it throws an exception instead of returning curses.ERR, which
I've dealt with by the simplest possible method of turning it back
into curses.ERR. (The exception in this case is almost always 'stdin
is nonblocking and there's nothing to see here yet'.)