prepare for deprecation of setLength in generator interface

Author: Robin Cawser

src/Vivait/StringGeneratorBundle/Model/GeneratorInterface.php

@@ -7,6 +7,8 @@ interface GeneratorInterface
     /**
      * @param integer $length
      * @return $this
+     * @deprecated this will be deprecated in version 2.0 in favour of using callbacks on the generator. This is due to
+     * some generators not actually needing a length - only random string type generators require it.
      */
     public function setLength($length);