Interface CommandLine.IExitCodeGenerator

@Command-annotated classes can implement this interface to specify an exit code that will be returned from the execute method when the command is successfully invoked.

Example usage:

 @Command
 class MyCommand implements Runnable, IExitCodeGenerator {
     public void run() { System.out.println("Hello"); }
     public int getExitCode() { return 123; }
 }
 CommandLine cmd = new CommandLine(new MyCommand());
 int exitCode = cmd.execute(args);
 assert exitCode == 123;
 System.exit(exitCode);