Add a customize mode where keys and options may be browsed and changed,

includes adding a brief description of each option. Bound to "C" by
default.

format.c

@@ -1392,7 +1392,7 @@ format_find(struct format_tree *ft, const char *key, int modifiers,
 	if (o == NULL)
 		o = options_parse_get(global_s_options, key, &idx, 0);
 	if (o != NULL) {
-		found = options_tostring(o, idx, 1);
+		found = options_to_string(o, idx, 1);
 		goto found;
 	}