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/AttrDef/HTML/Pixels.php

@@ -0,0 +1,76 @@
+<?php
+
+/**
+ * Validates an integer representation of pixels according to the HTML spec.
+ */
+class HTMLPurifier_AttrDef_HTML_Pixels extends HTMLPurifier_AttrDef
+{
+
+    /**
+     * @type int
+     */
+    protected $max;
+
+    /**
+     * @param int $max
+     */
+    public function __construct($max = null)
+    {
+        $this->max = $max;
+    }
+
+    /**
+     * @param string $string
+     * @param HTMLPurifier_Config $config
+     * @param HTMLPurifier_Context $context
+     * @return bool|string
+     */
+    public function validate($string, $config, $context)
+    {
+        $string = trim($string);
+        if ($string === '0') {
+            return $string;
+        }
+        if ($string === '') {
+            return false;
+        }
+        $length = strlen($string);
+        if (substr($string, $length - 2) == 'px') {
+            $string = substr($string, 0, $length - 2);
+        }
+        if (!is_numeric($string)) {
+            return false;
+        }
+        $int = (int)$string;
+
+        if ($int < 0) {
+            return '0';
+        }
+
+        // upper-bound value, extremely high values can
+        // crash operating systems, see <http://ha.ckers.org/imagecrash.html>
+        // WARNING, above link WILL crash you if you're using Windows
+
+        if ($this->max !== null && $int > $this->max) {
+            return (string)$this->max;
+        }
+        return (string)$int;
+    }
+
+    /**
+     * @param string $string
+     * @return HTMLPurifier_AttrDef
+     */
+    public function make($string)
+    {
+        if ($string === '') {
+            $max = null;
+        } else {
+            $max = (int)$string;
+        }
+        $class = get_class($this);
+        return new $class($max);
+    }
+}
+
+// vim: et sw=4 sts=4