Mautrix

* Stopped checking error message when checking if user is not registered on
whoami. Now it only requires the `M_FORBIDDEN` errcode instead of a specific
human-readable error message.
* Added handling for missing `unsigned` object in membership events
(thanks to [jevolk] in [39]).
* Added warning message when receiving encrypted messages with end-to-bridge
encryption disabled.
* Added utility for mutexes in caching async getters to prevent race conditions.

[jevolk]: https://github.com/jevolk
[39]: https://github.com/mautrix/python/pull/39

* Added handling for `M_NOT_FOUND` errors when getting pinned messages.
* Fixed bridge message send retrying so it always uses the same transaction ID.
* Fixed high-level `Client` class to automatically update state store with
events from sync.

* Added automatic login retry if double puppeting token is invalid on startup
or gets invalidated while syncing.
* Fixed ExtensibleEnum leaking keys between different types.
* Allowed changing bot used in ensure_joined.

* Changed attr deserialization errors to log full data instead of only known
fields when deserialization fails.

* Allowed `postgresql://` scheme in end-to-bridge encryption database URL
(in addition to `postgres://`).
* Slightly improved attr deserialization error messages.

* Changed end-to-bridge encryption to fail if homeserver doesn't advertise
appservice login. This breaks Synapse 1.21, but there have been plenty of
releases since then.
* Switched BaseFileConfig to use the built-in [pkgutil] instead of
pkg_resources (which requires setuptools).
* Added handling for `M_NOT_FOUND` errors when updating `m.direct` account data
through double puppeting in bridges.
* Added logging of data when attr deserializing fails.
* Exposed ExtensibleEnum in `mautrix.types` module.

[pkgutil]: https://docs.python.org/3/library/pkgutil.html