keyboard: Prefer lower keycodes

Xwayland can't handle keycodes above 255, so in order to play nice with X11,
we try to use the lowest possible keycode that's applicable for the given
shift level.

Fixes #148

src/keyboard.c

@@ -91,7 +91,7 @@ static int compare_symbols(const void* a, const void* b)
 	const struct table_entry* y = b;
 
 	if (x->symbol == y->symbol)
-		return x->level < y->level ? -1 : x->level > y->level;
+		return x->code < y->code ? -1 : x->code > y->code;
 
 	return x->symbol < y->symbol ? -1 : x->symbol > y->symbol;
 }