public function __construct($base_url = null, $config = 'en')
{
// Set defaults
$base_url = is_null($base_url) ? './' : $base_url;
// Set objet properties
$this->base_url = $this->setParam($base_url);
// Load configurations
$this->setConfiguration($config);
// load builders
$this->build_formats = $this->loadBuilders();
}