replaced Arg union with const char *arg, seems cleaner to me, even if we need atoi() in some places

main.c

@@ -236,7 +236,7 @@ sendevent(Window w, Atom a, long value) {
 }
 
 void
-quit(Arg arg) {
+quit(const char *arg) {
 	readin = running = False;
 }