Merge branch 'release-v0.18.0' of github.com:matrix-org/synapse

CHANGES.rst

docs/workers.rst

jenkins-dendron-postgres.sh

synapse/__init__.py

synapse/api/auth.py

synapse/app/appservice.py

synapse/app/client_reader.py

synapse/app/federation_reader.py

synapse/app/media_repository.py

synapse/app/pusher.py

synapse/app/synchrotron.py

synapse/appservice/api.py

synapse/config/server.py

synapse/events/snapshot.py

synapse/federation/federation_client.py

synapse/federation/federation_server.py

synapse/federation/transaction_queue.py

synapse/federation/transport/client.py

synapse/federation/transport/server.py

synapse/handlers/appservice.py