BREAKING: Add retryable arg to stage decorator

[jmgate]

It's a bit of a learning curve for those trying to create bare-bones staged scripts to see all those retry command line arguments automatically populated when they haven't designed their stages to be retryable. A better user experience would be to add a retryable flag to the stage() decorator and default it to False. Only if True do all those retry arguments get generated.

Note: This will be a breaking change.