Mautrix

* *(crypto)* Fixed error sharing megolm session if a single recipient device has ran out of one-time keys.

* **Breaking change *(util.async_db)*** Added checks to prevent calling `.start()` on a database multiple times.
* *(appservice)* Fixed [MSC2409] support to read to-device events from the correct field.
* *(appservice)* Added support for automatically calling functions when a transaction contains [MSC2409] to-device events or [MSC3202] encryption data.
* *(bridge)* Added option to use [MSC2409] and [MSC3202] for end-to-bridge encryption. However, this may not work with the Synapse implementation as it hasn't been tested yet.
* *(bridge)* Replaced `homeserver` -> `asmux` flag with more generic `software` field.
* *(bridge)* Added support for overriding parts of config with environment variables.
* If the value starts with `json::`, it'll be parsed as JSON instead of using as a raw string.
* *(client.api)* Added support for [MSC3870] for both uploading and downloading media.
* *(types)* Added `knock_restricted` join rule to `JoinRule` enum.
* *(crypto)* Added warning logs if claiming one-time keys for other users fails.

[MSC2409]: https://github.com/matrix-org/matrix-spec-proposals/pull/2409
[MSC3202]: https://github.com/matrix-org/matrix-spec-proposals/pull/3202
[MSC3870]: https://github.com/matrix-org/matrix-spec-proposals/pull/3870

* *(crypto)* Fixed parsing `/keys/claim` responses with no `failures` field.
* *(bridge)* Fixed parsing e2ee key sharing allow/minimum level config.

* *(util.async_db)* Added `init_commands` to run commands on each SQLite connection (e.g. to enable `PRAGMA`s). No-op on Postgres.
* *(bridge)* Added check to make sure e2ee keys are intact on server. If they aren't, the crypto database will be wiped and the bridge will stop.

* *(bridge)* Added hidden option to use appservice login for double puppeting.
* *(client)* Fixed sync handling throwing an error if event parsing failed.
* *(errors)* Added `M_UNKNOWN_ENDPOINT` error code from [MSC3743]
* *(appservice)* Updated [MSC3202] support to handle one time keys correctly.

[MSC3743]: https://github.com/matrix-org/matrix-spec-proposals/pull/3743
[MSC3202]: https://github.com/matrix-org/matrix-spec-proposals/pull/3202

* *(types)* Added `m.read.private` to receipt types.
* *(appservice)* Stopped `ensure_registered` and `invite_user` raising `IntentError`s (now they raise the original Matrix error instead).