Add 'CancellableAsyncCommand' for graceful CTRL + C termination #69

  // Customize help and error messages
                  config.SetExceptionHandler((ex, resolver) =>
                                             {
                                                 if (ex is InvalidOperationException && ex.Message.Contains("Configuration is incomplete"))
                                                 {
                                                     // Don't show the full exception for configuration errors
                                                     AnsiConsole.MarkupLine($"[red]{ex.Message}[/]");
                                                     return -1;
                                                 }

                                                 AnsiConsole.WriteException(ex);
                                                 return -1;
                                             });