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/options.c

@@ -833,6 +833,10 @@ int maxlen;
  * has the effect of 'meta'-ing the value which follows (so that the
  * alternate character set will be enabled).
  *
+ * X     normal key X
+ * ^X    control-X
+ * \mX   meta-X
+ *
  * For 3.4.3 and earlier, input ending with "\M", backslash, or caret
  * prior to terminating '\0' would pull that '\0' into the output and then
  * keep processing past it, potentially overflowing the output buffer.
@@ -3241,7 +3245,6 @@ boolean tinitial, tfrom_file;
             if (negated) {
                 bad_negation(fullname, FALSE);
             } else if ((op = string_for_opt(opts, FALSE)) != 0) {
-                int j;
                 char c, op_buf[BUFSZ];
 
                 escapes(op, op_buf);
@@ -3475,6 +3478,56 @@ boolean tinitial, tfrom_file;
     badoption(opts);
 }
 
+/* parse key:command */
+void
+parsebindings(bindings)
+char* bindings;
+{
+    char *bind;
+    char key;
+    int i;
+
+    /* break off first binding from the rest; parse the rest */
+    if ((bind = index(bindings, ',')) != 0) {
+        *bind++ = 0;
+        parsebindings(bind);
+    }
+
+    /* parse a single binding: first split around : */
+    if (! (bind = index(bindings, ':'))) return; /* it's not a binding */
+    *bind++ = 0;
+
+    /* read the key to be bound */
+    key = txt2key(bindings);
+    if (!key) {
+        raw_printf("Bad binding %s.", bindings);
+        wait_synch();
+        return;
+    }
+
+    bind = trimspaces(bind);
+
+    /* is it a special key? */
+    if (bind_specialkey(key, bind))
+        return;
+
+    /* is it a menu command? */
+    for (i = 0; i < NUM_MENU_CMDS; i++) {
+        if (!strcmp(default_menu_cmd_info[i].name, bind)) {
+            if (illegal_menu_cmd_key(key)) {
+                char tmp[BUFSZ];
+                Sprintf(tmp, "Bad menu key %s:%s", visctrl(key), bind);
+                badoption(tmp);
+            } else
+                add_menu_cmd_alias(key, default_menu_cmd_info[i].cmd);
+            return;
+        }
+    }
+
+    /* extended command? */
+    bind_key(key, bind);
+}
+
 static NEARDATA const char *menutype[] = { "traditional", "combination",
                                            "full", "partial" };