Define adapter behaviour.
See Maxwell.Adapter.Ibrowse.
Maxwell.Adapter.Ibrowse
return_t() :: Maxwell.Conn.t | {:error, any, Maxwell.Conn.t}
send_direct(Maxwell.Conn.t) :: return_t
send_file(Maxwell.Conn.t) :: return_t
send_multipart(Maxwell.Conn.t) :: return_t