* add phpunit as a dev dependency

* add some basic tests for UrlHelper::rewrite_relative()
 * fix UrlHelper::rewrite_relative() to work better on non-absolute
   relative URL paths

vendor/myclabs/deep-copy/src/DeepCopy/deep_copy.php

@@ -0,0 +1,20 @@
+<?php
+
+namespace DeepCopy;
+
+use function function_exists;
+
+if (false === function_exists('DeepCopy\deep_copy')) {
+    /**
+     * Deep copies the given value.
+     *
+     * @param mixed $value
+     * @param bool  $useCloneMethod
+     *
+     * @return mixed
+     */
+    function deep_copy($value, $useCloneMethod = false)
+    {
+        return (new DeepCopy($useCloneMethod))->copy($value);
+    }
+}