usage.go
func Usage(prefix string, spec interface{}) error {
	// The default is to output the usage information as a table
	// Create tabwriter instance to support table output
	tabs := tabwriter.NewWriter(os.Stdout, 1, 0, 4, ' ', 0)

	err := Usagef(prefix, spec, tabs, DefaultTableFormat)
	tabs.Flush()
	return err
}
func Usage(prefix string, spec interface{}) error {
	// The default is to output the usage information as a table
	// Create tabwriter instance to support table output
	tabs := tabwriter.NewWriter(os.Stdout, 1, 0, 4, ' ', 0)

	err := Usagef(prefix, spec, tabs, DefaultTableFormat)
	tabs.Flush()
	return err
}
// Usage writes usage information to stderr using the default header and table format