Added diff method to AuditReaderInterface

Model/AuditReaderInterface.php

@@ -38,4 +38,12 @@ interface AuditReaderInterface
      * @param string $id
      */
     public function findRevisions($className, $id);
+
+    /**
+     * @param string $className
+     * @param int $id
+     * @param int $oldRevision
+     * @param int $newRevision
+     */
+    public function diff($className, $id, $oldRevision, $newRevision);
 }