Added SPL Queue example

Author: Alienpruts

chap-04/SplQueue.php

@@ -0,0 +1,19 @@
+<?php
+/**
+ * Created by PhpStorm.
+ * User: bert
+ * Date: 3/10/18
+ * Time: 22:39
+ */
+
+$agents = new SplQueue();
+
+$agents->enqueue("Fred");
+$agents->enqueue("John");
+$agents->enqueue("Keith");
+$agents->enqueue("Adiyan");
+$agents->enqueue("Michael");
+
+echo $agents->dequeue() . PHP_EOL;
+echo $agents->dequeue() . PHP_EOL;
+echo $agents->bottom() . PHP_EOL;