It should be possible to provide the payload as a struct

[Kuzmin]

I often find myself submitting JSON payloads to REST API's, but this library currently only allows for payloads in the form of url.Values.

Are PR's welcome?

[xiam]

Hello @Kuzmin,

Most of the time I just use PostRaw() or PutRaw() since they accept []byte, and this []byte can be easily generated from a struct. Adding the ability to both of them to use either []byte or a encoding.TextMarshaler also sounds good to me.