add transport codec

transport/codec/codec.go

@@ -0,0 +1,10 @@
+package codec
+
+// Codec is used for encoding where the transport doesn't natively support
+// headers in the message type. In this case the entire message is
+// encoded as the payload
+type Codec interface {
+	Marshal(interface{}) ([]byte, error)
+	Unmarshal([]byte, interface{}) error
+	String() string
+}