* 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
* started work on sync package
* send getaddr on connect
* fixed node_table insert, added insert_many
* addr protocol
* sync headers response
* continue sync
* continue sync protocol
* separated sync connection start from sync connection creation
* switched to getblocks (instead of getheaders)
* starting to receive blocks in sync
* deal with orphaned blocks in sync::local_chain
* continue sync
* fix warnings
* removed TODOs
* protocol::sync is back to private state
* fixed grumbes
NikVolf
Svyatoslav Nikolsky