Implement ostream operator<< for RsSerializable

So it is not necessary to define it for each class we want to print in
  debug

libretroshare/src/serialiser/rsserializable.h

@@ -20,8 +20,11 @@
  *                                                                             *
  *******************************************************************************/
 #pragma once
+
 #include "serialiser/rsserializer.h"
 
+#include <iosfwd>
+
 
 /** @brief Minimal ancestor for all serializable structs in RetroShare.
  * If you want your struct to be easly serializable you should inherit from this
@@ -49,3 +52,5 @@ struct RsSerializable
 #define RS_SERIAL_PROCESS(I) do { \
 	RsTypeSerializer::serial_process(j, ctx, I, #I ); \
 	} while(0)
+
+std::ostream &operator<<(std::ostream& out, const RsSerializable& serializable);