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/Target.php

@@ -0,0 +1,23 @@
+<?php
+
+/**
+ * XHTML 1.1 Target Module, defines target attribute in link elements.
+ */
+class HTMLPurifier_HTMLModule_Target extends HTMLPurifier_HTMLModule
+{
+
+    public $name = 'Target';
+
+    public function setup($config) {
+        $elements = array('a');
+        foreach ($elements as $name) {
+            $e = $this->addBlankElement($name);
+            $e->attr = array(
+                'target' => new HTMLPurifier_AttrDef_HTML_FrameTarget()
+            );
+        }
+    }
+
+}
+
+// vim: et sw=4 sts=4