subcommands.go
func Execute(ctx context.Context, args ...interface{}) ExitStatus {
	return DefaultCommander.Execute(ctx, args...)
}
func Execute(ctx context.Context, args ...interface{}) ExitStatus {
	return DefaultCommander.Execute(ctx, args...)
}
// Execute should be called once the default flags have been
// initialized by flag.Parse. It finds the correct subcommand and
// executes it, and returns an ExitStatus with the result. On a usage
// error, an appropriate message is printed to os.Stderr, and
// ExitUsageError is returned. The additional args are provided as-is
// to the Execute method of the selected Command. It is a wrapper
// around DefaultCommander.Execute.