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/StringHash.php

@@ -0,0 +1,39 @@
+<?php
+
+/**
+ * This is in almost every respect equivalent to an array except
+ * that it keeps track of which keys were accessed.
+ *
+ * @warning For the sake of backwards compatibility with early versions
+ *     of PHP 5, you must not use the $hash[$key] syntax; if you do
+ *     our version of offsetGet is never called.
+ */
+class HTMLPurifier_StringHash extends ArrayObject
+{
+    protected $accessed = array();
+
+    /**
+     * Retrieves a value, and logs the access.
+     */
+    public function offsetGet($index) {
+        $this->accessed[$index] = true;
+        return parent::offsetGet($index);
+    }
+
+    /**
+     * Returns a lookup array of all array indexes that have been accessed.
+     * @return Array in form array($index => true).
+     */
+    public function getAccessed() {
+        return $this->accessed;
+    }
+
+    /**
+     * Resets the access array.
+     */
+    public function resetAccessed() {
+        $this->accessed = array();
+    }
+}
+
+// vim: et sw=4 sts=4