* 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/nikic/php-parser/lib/PhpParser/NodeVisitorAbstract.php

@@ -0,0 +1,25 @@
+<?php declare(strict_types=1);
+
+namespace PhpParser;
+
+/**
+ * @codeCoverageIgnore
+ */
+class NodeVisitorAbstract implements NodeVisitor
+{
+    public function beforeTraverse(array $nodes) {
+        return null;
+    }
+
+    public function enterNode(Node $node) {
+        return null;
+    }
+
+    public function leaveNode(Node $node) {
+        return null;
+    }
+
+    public function afterTraverse(array $nodes) {
+        return null;
+    }
+}