Replace existing autoloader with Composer-supplied

- Move Friendica namespace to `src`
- Move required `ezyang/htmlpurifier` to vendor
- Remove existing static autoloader
- Change boot.php reference to the autoloader

vendor/ezyang/htmlpurifier/library/HTMLPurifier/EntityLookup.php

@@ -0,0 +1,48 @@
+<?php
+
+/**
+ * Object that provides entity lookup table from entity name to character
+ */
+class HTMLPurifier_EntityLookup
+{
+    /**
+     * Assoc array of entity name to character represented.
+     * @type array
+     */
+    public $table;
+
+    /**
+     * Sets up the entity lookup table from the serialized file contents.
+     * @param bool $file
+     * @note The serialized contents are versioned, but were generated
+     *       using the maintenance script generate_entity_file.php
+     * @warning This is not in constructor to help enforce the Singleton
+     */
+    public function setup($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 bool|HTMLPurifier_EntityLookup $prototype Optional prototype of custom lookup table to overload with.
+     * @return HTMLPurifier_EntityLookup
+     */
+    public static function instance($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