Added Laurent's tests/model save() method

lib/Models/Model.php

@@ -8,4 +8,12 @@ class Model extends \Sudzy\ValidModel {
     $customValidators = new CustomValidator();
     parent::__construct($customValidators->init());
   }
+
+  function save() {
+    if ($this->created_at === null) {
+      $this->created_at = date("Y-m-d H:i:s");
+    }
+    parent::save();
+  }
+
 }