Fix response RID with postDocument method

Changes in files: CurlClientResponse.php (I added STATUS_CREATED to getValidStatusCodes() method) and CurlClientAdapterResult.php (I added isValidRid method which checks if response is valid RID and changed getData() method). With those changes if i'm doing something like this:
$response = $this->container->get('orientdb.binding')->postDocument(json_encode($object));  
$rid = $response->getData();
I have returned valid RID from OrientDB. Without those changes I have only NULL :(