protected function registerMarkdownEngine($resolver)
    {
        $app = $this->app;

        $app->singleton('markdown.compiler', function ($app) {
            $cache = $app['config']['view.compiled'];

            return new MarkdownCompiler($app['files'], $cache);
        });

        $resolver->register('markdown', function () use ($app) {
            return new MarkdownEngine($app['markdown.compiler'], $app['files']);
        });

        $app['view']->addExtension('md', 'markdown');
    }