Merge pull request #2082 from matrix-org/erikj/repl_tcp_server

docs/tcp_replication.rst

synapse/app/homeserver.py

synapse/federation/send_queue.py

synapse/handlers/presence.py

synapse/handlers/typing.py

synapse/notifier.py

synapse/replication/resource.py

synapse/replication/tcp/__init__.py

synapse/replication/tcp/commands.py

synapse/replication/tcp/protocol.py

synapse/replication/tcp/resource.py

synapse/replication/tcp/streams.py

synapse/storage/devices.py

synapse/storage/events.py

synapse/storage/pusher.py