Add fluent email priority setter.

src/Illuminate/Mail/Mailable.php

@@ -340,6 +340,23 @@ public function replyTo($address, $name = null)
         return $this->setAddress($address, $name, 'replyTo');
     }
 
+    /**
+     * Set the priority of this message.
+     *
+     * The value is an integer where 1 is the highest priority and 5 is the lowest.
+     *
+     * @param  int  $level
+     * @return $this
+     */
+    public function priority($level = 3)
+    {
+        $this->callbacks[] = function ($message) use ($level) {
+            $message->setPriority($level);
+        };
+
+        return $this;
+    }
+
     /**
      * Set the recipients of the message.
      *