app.enable('autoupdate') option support

lib/railway.js

@@ -93,9 +93,13 @@ function loadSchema(schema, railway, app, models) {
         fn(context, require);
     }
 
-    // and freeze schemas
+    // autoupdate if set app.enable('autoupdate')  or freeze schemas by default
     railway.orm._schemas.forEach(function (schema) {
-        schema.freeze();
+        if(app.enabled('autoupdate')){
+            schema.autoupdate();
+        } esle {
+            schema.freeze();
+        }
     });
 }