Crawls all unique links.
$urls = (new Centipede\Crawler('http://dev.umpirsky.com'))->crawl();
(new Centipede\Crawler('http://dev.umpirsky.com'))->crawl(function ($url, GuzzleHttp\Message\FutureResponse $response) {
printf('(%d) %s', $response->getStatusCode(), $url);
});