Add key rebinding

This is a modified version of Jason Dorje Short's key rebinding
patch, and allows also binding special keys, such as the ones
used in getloc and getpos.

One of the ways to play NetHack on nethack.alt.org is via a HTML
terminal in browser. Unfortunately this means several ctrl-key
combinations cannot be entered, because the browser intercepts
those. Similar thing applies to some international keyboard layouts
on Windows. With this patch, the user can just rebind the command
to a key that works best for them.

I've tested this on Linux TTY, X11, and Windows TTY and GUI.

src/allmain.c

@@ -34,9 +34,6 @@ boolean resuming;
     monstr_init(); /* monster strengths */
     objects_init();
 
-    if (wizard)
-        add_debug_extended_commands();
-
     /* if a save file created in normal mode is now being restored in
        explore mode, treat it as normal restore followed by 'X' command
        to use up the save file and require confirmation for explore mode */