public function registerArgument($arg, $help, $required = true, $command = '')
    {
        if (!isset($this->setup[$command])) {
            throw new Exception("Command $command not registered");
        }

        $this->setup[$command]['args'][] = array(
            'name' => $arg,
            'help' => $help,
            'required' => $required
        );
    }