feat: custom error mgs with tag (generic function)

[thanhphuchuynh]

Customizing Error Messages with Tags

In addition to specifying constraints for struct fields, we can also customize error messages using tags. To do this, we add a message tag to our struct field tags.

type PaymentInfo struct {
    CreditCardNumber string `validate:"required" errormgs:"Invalid credit card is required xxx"`
    CVV              string `validate:"required,len=3" errormgs:"CVV code must be three digits long"`
}

[coveralls]

coverage: 73.967% (-0.005%) from 73.972% when pulling cba5d11 on ThanhPhucHuynh:feat/errortag into bd1113d on go-playground:master.