Mautrix

* *(crypto)* Changed `OlmMachine.share_keys` to make the OTK count parameter
optional. When omitted, the count is fetched from the server.
* *(appservice)* Added option to run appservice transaction event handlers
synchronously.
* *(appservice)* Added `log` and `hs_token` parameters to `AppServiceServerMixin`
to allow using it as a standalone class without extending.
* *(api)* Added support for setting appservice `user_id` and `device_id` query
parameters manually without using `AppServiceAPI`.

* *(util.program)* Removed `--base-config` flag in bridges, as there are no
valid use cases (package data should always work) and it's easy to cause
issues by pointing the flag at the wrong file.
* *(bridge)* Added support for the `com.devture.shared_secret_auth` login type
for automatic double puppeting.
* *(bridge)* Dropped support for syncing with double puppets. MSC2409 is now
the only way to receive ephemeral events.
* *(bridge)* Added support for double puppeting with arbitrary `as_token`s.

* Dropped Python 3.8 support.
* **Breaking change *(.state_store)*** Removed legacy SQLAlchemy state store
implementations.
* **Mildly breaking change *(util.async_db)*** Changed `SQLiteDatabase` to not
remove prefix slashes from database paths.
* Library users should use `sqlite:path.db` instead of `sqlite:///path.db`
for relative paths, and `sqlite:/path.db` instead of `sqlite:////path.db`
for absolute paths.
* Bridge configs do this migration automatically.
* *(util.async_db)* Added warning log if using SQLite database path that isn't
writable.
* *(util.program)* Fixed `manual_stop` not working if it's called during startup.
* *(client)* Stabilized support for asynchronous uploads.
* `unstable_create_msc` was renamed to `create_mxc`, and the `max_stall_ms`
parameters for downloading were renamed to `timeout_ms`.
* *(crypto)* Added option to not rotate keys when devices change.
* *(crypto)* Added option to remove all keys that were received before the
automatic ratcheting was implemented (in v0.19.10).
* *(types)* Improved reply fallback removal to have a smaller chance of false
positives for messages that don't use reply fallbacks.

* *(appservice)* Fixed Python 3.8 compatibility.

* *(client)* Fixed dispatching room ephemeral events (i.e. typing notifications) in syncer.

* *(bridge)* Implemented appservice pinging using MSC2659.
* *(bridge)* Started reusing aiosqlite connection pool for crypto db.
* This fixes the crypto pool getting stuck if the bridge exits unexpectedly
(the default pool is closed automatically at any type of exit).