Fix #567: Add proxy support for MultiCurl

examples/multi_curl_proxy.php

@@ -0,0 +1,13 @@
+<?php
+require __DIR__ . '/../vendor/autoload.php';
+
+use \Curl\Curl;
+
+$multi_curl = new MultiCurl();
+$multi_curl->setProxy('someproxy.com', '9999', 'username', 'password');
+$multi_curl->setProxyTunnel();
+$multi_curl->addGet('https://httpbin.org/ip');
+$multi_curl->complete(function ($instance) {
+    var_dump($instance->response);
+});
+$multi_curl->start();