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/EntityLookup.php

@@ -0,0 +1,44 @@
+<?php
+
+/**
+ * Object that provides entity lookup table from entity name to character
+ */
+class HTMLPurifier_EntityLookup {
+
+    /**
+     * Assoc array of entity name to character represented.
+     */
+    public $table;
+
+    /**
+     * Sets up the entity lookup table from the serialized file contents.
+     * @note The serialized contents are versioned, but were generated
+     *       using the maintenance script generate_entity_file.php
+     * @warning This is not in constructor to help enforce the Singleton
+     */
+    public function setup($file = false) {
+        if (!$file) {
+            $file = HTMLPURIFIER_PREFIX . '/HTMLPurifier/EntityLookup/entities.ser';
+        }
+        $this->table = unserialize(file_get_contents($file));
+    }
+
+    /**
+     * Retrieves sole instance of the object.
+     * @param Optional prototype of custom lookup table to overload with.
+     */
+    public static function instance($prototype = false) {
+        // no references, since PHP doesn't copy unless modified
+        static $instance = null;
+        if ($prototype) {
+            $instance = $prototype;
+        } elseif (!$instance) {
+            $instance = new HTMLPurifier_EntityLookup();
+            $instance->setup();
+        }
+        return $instance;
+    }
+
+}
+
+// vim: et sw=4 sts=4