* p2p <-> sync interfaces proposal
* updated with example
* send errors will be handled in p2p module => no need to return to the sync
* poc of outbound sync connection
* simplified send_to_peer
* context has cpu pool and enent loop handles
* on_message won't return ProtocolAction anymore
* session initialized sync protocol, remove retain cycles on P2P::drop
* removed ProtocolAction
* uncommented ping protocol
* node_table sorts nodes also by recently used time
* send getaddr on connect
* fixed node_table insert, added insert_many
* addr protocol
* added TODO: remove