Add website to client repository

Closes #1567

The main reason I'm not simply merging Annika's PR is because this
way makes it clearer that I'm taking responsibility for all this
code, that it's mostly code I wrote, and also because it makes it
easier to ensure that none of the files have been changed.

(Not that I don't personally trust Annika, but I have something
resembling an obligation to users not to expose them to risks based
on personal trust.)

website/lib/htmlpurifier/HTMLPurifier/HTMLModule/TargetBlank.php

@@ -0,0 +1,19 @@
+<?php
+
+/**
+ * Module adds the target=blank attribute transformation to a tags.  It
+ * is enabled by HTML.TargetBlank
+ */
+class HTMLPurifier_HTMLModule_TargetBlank extends HTMLPurifier_HTMLModule
+{
+
+    public $name = 'TargetBlank';
+
+    public function setup($config) {
+        $a = $this->addBlankElement('a');
+        $a->attr_transform_post[] = new HTMLPurifier_AttrTransform_TargetBlank();
+    }
+
+}
+
+// vim: et sw=4 sts=4