Support configure tag when marshal/unmarshal

For example, I have a struct as follows， I want the id field to be omitted in json when writing http response， so I set tag json:"-", it's ok。 But when I want to marshal the same struct to redis (or unmarshal from redis) , I want the id field not to be omitted .So would you please allow developers to decide whether to ignore tag when marshal/unmarshal

type Example struct { Id int64 json:"-" IdStr string json:"id" }