public function get($key, $options = null, $default = null, $filter = null)
    {
        $value = $default;
        if (is_array($options) && array_key_exists($key, $options)) {
            $value = $options[$key];
        } elseif (array_key_exists($key, $this->config)) {
            $value = $this->config[$key];
        }
        if (is_callable($filter)) {
            $filter($value);
        }
        return $value;
    }