code: func (k APIKey) MarshalJSON() ([]byte, error) {
  	// Approach for custom (un)marshalling borrowed from http://choly.ca/post/go-json-marshalling/
  	type Alias APIKey
  	return json.Marshal(&struct {
  		Created *string `json:"created,omitempty"`
  		*Alias
  	}{
  		Created: String(k.Created.Format(createdTimeLayout)),
  		Alias:   (*Alias)(&k),
  	})
  }
docs: // MarshalJSON is a custom method for handling datetime marshalling