func (v *Validate) AddFunction(key string, f Func) error {

	if len(key) == 0 {
		return errors.New("Function Key cannot be empty")
	}

	if f == nil {
		return errors.New("Function cannot be empty")
	}

	v.validationFuncs[key] = f

	return nil
}
func (v *Validate) AddFunction(key string, f Func) error {

	if len(key) == 0 {
		return errors.New("Function Key cannot be empty")
	}

	if f == nil {
		return errors.New("Function cannot be empty")
	}

	v.validationFuncs[key] = f

	return nil
}
// AddFunction adds a validation Func to a Validate's map of validators denoted by the key
// NOTE: if the key already exists, it will get replaced.
// NOTE: this method is not thread-safe