type Data interface {
// Content returns the data as a value that can be processed by encoders such as "encoding/json" Content(template, language string) (interface{}, error)
// Headers returns response headers relating to the data (optional) Headers() map[string]string
}
With returns a copy of v with extra headers attached. These are passed in as key+value pairs.
The header names should be in normal form, e.g. "Last-Modified" instead of "last-modified",
but this is not mandatory.