…bership_join_count

* 'develop' of github.com:matrix-org/synapse:
  Update workers docs (#7990)
  Fix invite rejection when we have no forward-extremeties (#7980)
  Fix typo in docs/workers.md (#7992)
  Convert federation client to async/await. (#7975)
  Convert appservice to async. (#7973)
  Convert some of the data store to async. (#7976)
  Fix formatting of changelog and upgrade notes
  Ensure that remove_pusher is always async (#7981)
  Add deprecation warnings
  1.18.0
  Update worker docs with recent enhancements  (#7969)
  Ensure the msg property of HttpResponseException is a string. (#7979)
  Remove from the event_relations table when purging historical events. (#7978)
  Add additional logging for SAML sessions. (#7971)
  Add MSC reference to changelog for #7736
  Re-implement unread counts (#7736)
  Various improvements to the docs (#7899)

Synapse 1.19.0rc1 (2020-08-13)
==============================

Removal warning
---------------

As outlined in the [previous release](https://github.com/matrix-org/synapse/releases/tag/v1.18.0), we are no longer publishing Docker images with the `-py3` tag suffix. On top of that, we have also removed the `latest-py3` tag. Please see [the announcement in the upgrade notes for 1.18.0](https://github.com/matrix-org/synapse/blob/develop/UPGRADE.rst#upgrading-to-v1180).

Features
--------

- Add option to allow server admins to join rooms which fail complexity checks. Contributed by @lugino-emeritus. ([\#7902](#7902))
- Add an option to purge room or not with delete room admin endpoint (`POST /_synapse/admin/v1/rooms/<room_id>/delete`). Contributed by @dklimpel. ([\#7964](#7964))
- Add rate limiting to users joining rooms. ([\#8008](#8008))
- Add a `/health` endpoint to every configured HTTP listener that can be used as a health check endpoint by load balancers. ([\#8048](#8048))
- Allow login to be blocked based on the values of SAML attributes. ([\#8052](#8052))
- Allow guest access to the `GET /_matrix/client/r0/rooms/{room_id}/members` endpoint, according to MSC2689. Contributed by Awesome Technologies Innovationslabor GmbH. ([\#7314](#7314))

Bugfixes
--------

- Fix a bug introduced in Synapse v1.7.2 which caused inaccurate membership counts in the room directory. ([\#7977](#7977))
- Fix a long standing bug: 'Duplicate key value violates unique constraint "event_relations_id"' when message retention is configured. ([\#7978](#7978))
- Fix "no create event in auth events" when trying to reject invitation after inviter leaves. Bug introduced in Synapse v1.10.0. ([\#7980](#7980))
- Fix various comments and minor discrepencies in server notices code. ([\#7996](#7996))
- Fix a long standing bug where HTTP HEAD requests resulted in a 400 error. ([\#7999](#7999))
- Fix a long-standing bug which caused two copies of some log lines to be written when synctl was used along with a MemoryHandler logger. ([\#8011](#8011), [\#8012](#8012))

Updates to the Docker image
---------------------------

- We no longer publish Docker images with the `-py3` tag suffix, as [announced in the upgrade notes](https://github.com/matrix-org/synapse/blob/develop/UPGRADE.rst#upgrading-to-v1180). ([\#8056](#8056))

Improved Documentation
----------------------

- Document how to set up a client .well-known file and fix several pieces of outdated documentation. ([\#7899](#7899))
- Improve workers docs. ([\#7990](#7990), [\#8000](#8000))
- Fix typo in `docs/workers.md`. ([\#7992](#7992))
- Add documentation for how to undo a room shutdown. ([\#7998](#7998), [\#8010](#8010))

Internal Changes
----------------

- Reduce the amount of whitespace in JSON stored and sent in responses. Contributed by David Vo. ([\#7372](#7372))
- Switch to the JSON implementation from the standard library and bump the minimum version of the canonicaljson library to 1.2.0. ([\#7936](#7936), [\#7979](#7979))
- Convert various parts of the codebase to async/await. ([\#7947](#7947), [\#7948](#7948), [\#7949](#7949), [\#7951](#7951), [\#7963](#7963), [\#7973](#7973), [\#7975](#7975), [\#7976](#7976), [\#7981](#7981), [\#7987](#7987), [\#7989](#7989), [\#8003](#8003), [\#8014](#8014), [\#8016](#8016), [\#8027](#8027), [\#8031](#8031), [\#8032](#8032), [\#8035](#8035), [\#8042](#8042), [\#8044](#8044), [\#8045](#8045), [\#8061](#8061), [\#8062](#8062), [\#8063](#8063), [\#8066](#8066), [\#8069](#8069), [\#8070](#8070))
- Move some database-related log lines from the default logger to the database/transaction loggers. ([\#7952](#7952))
- Add a script to detect source code files using non-unix line terminators. ([\#7965](#7965), [\#7970](#7970))
- Log the SAML session ID during creation. ([\#7971](#7971))
- Implement new experimental push rules for some users. ([\#7997](#7997))
- Remove redundant and unreliable signature check for v1 Identity Service lookup responses. ([\#8001](#8001))
- Improve the performance of the register endpoint. ([\#8009](#8009))
- Reduce less useful output in the newsfragment CI step. Add a link to the changelog section of the contributing guide on error. ([\#8024](#8024))
- Rename storage layer objects to be more sensible. ([\#8033](#8033))
- Change the default log config to reduce disk I/O and storage for new servers. ([\#8040](#8040))
- Add an assertion on `prev_events` in `create_new_client_event`. ([\#8041](#8041))
- Add a comment to `ServerContextFactory` about the use of `SSLv23_METHOD`. ([\#8043](#8043))
- Log `OPTIONS` requests at `DEBUG` rather than `INFO` level to reduce amount logged at `INFO`. ([\#8049](#8049))
- Reduce amount of outbound request logging at `INFO` level. ([\#8050](#8050))
- It is no longer necessary to explicitly define `filters` in the logging configuration. (Continuing to do so is redundant but harmless.) ([\#8051](#8051))
- Add and improve type hints. ([\#8058](#8058), [\#8064](#8064), [\#8060](#8060), [\#8067](#8067))

* commit 'b3a97d6da':
  Convert some of the data store to async. (#7976)