Add getCode() to ResponseInterface. Closes #25

Author: amacneil

src/Omnipay/Common/Message/AbstractResponse.php

@@ -50,6 +50,11 @@ public function getMessage()
         return null;
     }
 
+    public function getCode()
+    {
+        return null;
+    }
+
     public function getTransactionReference()
     {
         return null;

src/Omnipay/Common/Message/ResponseInterface.php

@@ -44,6 +44,13 @@ public function isRedirect();
      */
     public function getMessage();
 
+    /**
+     * Response code
+     *
+     * @return string A response code from the payment gateway
+     */
+    public function getCode();
+
     /**
      * Gateway Reference
      *