func RegisterOptional(name string, fn MigrateFunc) error {
	return register(name, true, fn)
}
func RegisterOptional(name string, fn MigrateFunc) error {
	return register(name, true, fn)
}
func RegisterOptional ( name string , fn MigrateFunc ) error { return register ( name , true , fn ) }
// RegisterOptional register a new migration that will not run automatically
// when calling the Run funcition.
RegisterOptional register a new migration that will not run automatically when calling the Run funcition .