Added a TagProcessor

The TagProcessor adds the tags key to the record making it so that it can be used by handlers like Raven.

src/Monolog/Processor/TagProcessor.php

@@ -0,0 +1,37 @@
+<?php
+
+/*
+ * This file is part of the Monolog package.
+ *
+ * (c) Jordi Boggiano <j.boggiano@seld.be>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Monolog\Processor;
+
+/**
+ * Adds a tags array into record
+ *
+ * @author Martijn Riemers
+ */
+class TagProcessor
+{
+    private $tags;
+
+    public function __construct(array $tags = array())
+    {
+        $this->tags = $tags;
+    }
+
+    public function __invoke(array $record)
+    {
+        $record['tags'] = array_merge(
+            $this->tags,
+            $record['tags']
+        );
+
+        return $record;
+    }
+}