Use constants for the command status code

Author: javiereguiluz

components/console/helpers/questionhelper.rst

@@ -40,7 +40,7 @@ the following to your command::
             $question = new ConfirmationQuestion('Continue with this action?', false);
 
             if (!$helper->ask($input, $output, $question)) {
-                return 0;
+                return Command::SUCCESS;
             }
         }
     }

console/commands_as_services.rst

@@ -45,8 +45,8 @@ For example, suppose you want to log something from within your command::
         {
             $this->logger->info('Waking up the sun');
             // ...
-            
-            return 0;
+
+            return Command::SUCCESS;
         }
     }
 

console/input.rst

@@ -52,8 +52,8 @@ You now have access to a ``last_name`` argument in your command::
             }
 
             $output->writeln($text.'!');
-            
-            return 0;
+
+            return Command::SUCCESS;
         }
     }