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/VarParser/Native.php

@@ -0,0 +1,38 @@
+<?php
+
+/**
+ * This variable parser uses PHP's internal code engine. Because it does
+ * this, it can represent all inputs; however, it is dangerous and cannot
+ * be used by users.
+ */
+class HTMLPurifier_VarParser_Native extends HTMLPurifier_VarParser
+{
+
+    /**
+     * @param mixed $var
+     * @param int $type
+     * @param bool $allow_null
+     * @return null|string
+     */
+    protected function parseImplementation($var, $type, $allow_null)
+    {
+        return $this->evalExpression($var);
+    }
+
+    /**
+     * @param string $expr
+     * @return mixed
+     * @throws HTMLPurifier_VarParserException
+     */
+    protected function evalExpression($expr)
+    {
+        $var = null;
+        $result = eval("\$var = $expr;");
+        if ($result === false) {
+            throw new HTMLPurifier_VarParserException("Fatal error in evaluated code");
+        }
+        return $var;
+    }
+}
+
+// vim: et sw=4 sts=4