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/URI.php

@@ -0,0 +1,111 @@
+<?php
+
+/**
+ * Validates a URI as defined by RFC 3986.
+ * @note Scheme-specific mechanics deferred to HTMLPurifier_URIScheme
+ */
+class HTMLPurifier_AttrDef_URI extends HTMLPurifier_AttrDef
+{
+
+    /**
+     * @type HTMLPurifier_URIParser
+     */
+    protected $parser;
+
+    /**
+     * @type bool
+     */
+    protected $embedsResource;
+
+    /**
+     * @param bool $embeds_resource Does the URI here result in an extra HTTP request?
+     */
+    public function __construct($embeds_resource = false)
+    {
+        $this->parser = new HTMLPurifier_URIParser();
+        $this->embedsResource = (bool)$embeds_resource;
+    }
+
+    /**
+     * @param string $string
+     * @return HTMLPurifier_AttrDef_URI
+     */
+    public function make($string)
+    {
+        $embeds = ($string === 'embedded');
+        return new HTMLPurifier_AttrDef_URI($embeds);
+    }
+
+    /**
+     * @param string $uri
+     * @param HTMLPurifier_Config $config
+     * @param HTMLPurifier_Context $context
+     * @return bool|string
+     */
+    public function validate($uri, $config, $context)
+    {
+        if ($config->get('URI.Disable')) {
+            return false;
+        }
+
+        $uri = $this->parseCDATA($uri);
+
+        // parse the URI
+        $uri = $this->parser->parse($uri);
+        if ($uri === false) {
+            return false;
+        }
+
+        // add embedded flag to context for validators
+        $context->register('EmbeddedURI', $this->embedsResource);
+
+        $ok = false;
+        do {
+
+            // generic validation
+            $result = $uri->validate($config, $context);
+            if (!$result) {
+                break;
+            }
+
+            // chained filtering
+            $uri_def = $config->getDefinition('URI');
+            $result = $uri_def->filter($uri, $config, $context);
+            if (!$result) {
+                break;
+            }
+
+            // scheme-specific validation
+            $scheme_obj = $uri->getSchemeObj($config, $context);
+            if (!$scheme_obj) {
+                break;
+            }
+            if ($this->embedsResource && !$scheme_obj->browsable) {
+                break;
+            }
+            $result = $scheme_obj->validate($uri, $config, $context);
+            if (!$result) {
+                break;
+            }
+
+            // Post chained filtering
+            $result = $uri_def->postFilter($uri, $config, $context);
+            if (!$result) {
+                break;
+            }
+
+            // survived gauntlet
+            $ok = true;
+
+        } while (false);
+
+        $context->destroy('EmbeddedURI');
+        if (!$ok) {
+            return false;
+        }
+        // back to string
+        return $uri->toString();
+    }
+}
+
+// vim: et sw=4 sts=4