Mautrix

* *(util.ffmpeg)* Added simple utility module that wraps ffmpeg and tempfiles
to convert audio/video files to different formats, primarily intended for
bridging. FFmpeg must be installed separately and be present in `$PATH`.

* **Breaking change *(mautrix.util.formatter)*** Made `MatrixParser` async
and non-static.
* Being async is necessary for bridges that need to make database calls to
convert mentions (e.g. Telegram has username mentions, which can't be
extracted from the Matrix user ID).
* Being non-static allows passing additional context into the formatter by
extending the class and setting instance variables.
* *(util.formatter)* Added support for parsing
[spoilers](https://spec.matrix.org/v1.1/client-server-api/#spoiler-messages).
* *(crypto.olm)* Added `describe` method for `OlmSession`s.
* *(crypto)* Fixed sorting Olm sessions (now sorted by last successful decrypt
time instead of alphabetically by session ID).
* *(crypto.store.asyncpg)* Fixed caching Olm sessions so that using the same
session twice wouldn't cause corruption.
* *(crypto.attachments)* Added support for decrypting files from
non-spec-compliant clients (e.g. FluffyChat) that have a non-zero counter
part in the AES initialization vector.
* *(util.async_db)* Added support for using Postgres positional param syntax in
the async SQLite helper (by regex-replacing `$<number>` with `?<number>`).
* *(util.async_db)* Added wrapper methods for `executemany` in `Database` and
aiosqlite `TxnConnection`.
* *(bridge)* Changed portal cleanup to leave and forget rooms using double
puppeting instead of just kicking the user.

* Fixed type hints in the `mautrix.crypto.store` module.
* Added debug logs for detecting crypto sync handling slowness.

* Switched message double puppet indicator convention from
`"net.maunium.<bridge_type>.puppet": true` to `"fi.mau.double_puppet_source": "<bridge_type>"`.
* Added double puppet indicator to redactions made with `IntentAPI.redact`.

* Changed lack of media encryption dependencies (pycryptodome) to be a fatal
error like lack of normal encryption dependencies (olm) are in v0.13.0.
* Added base methods for implementing relay mode in bridges
(started by [Alejo0290] in [72]).

[Alejo0290]: https://github.com/Alejo0290
[72]: https://github.com/mautrix/python/pull/72

* Formatted all code using [black](https://github.com/psf/black)
and [isort](https://github.com/PyCQA/isort).
* Added `power_level_override` parameter to `ClientAPI.create_room`.
* Added default implementations of `delete-portal` and `unbridge` commands for bridges
* Added automatic Olm session recreation if an incoming message fails to decrypt.
* Added automatic key re-requests in bridges if the Megolm session doesn't arrive on time.
* Changed `ClientAPI.send_text` to parse the HTML to generate a plaintext body
instead of using the HTML directly when a separate plaintext body is not
provided (also affects `send_notice` and `send_emote`).
* Changed lack of encryption dependencies to be a fatal error if encryption is
enabled in bridge config.
* Fixed `StoreUpdatingAPI` not updating the local state store when using
friendly membership methods like `kick_user`.
* Switched Bridge class to use async_db (asyncpg/aiosqlite) instead of the
legacy SQLAlchemy db by default.
* Removed deprecated `ClientAPI.parse_mxid` method
(use `ClientAPI.parse_user_id` instead).
* Renamed `ClientAPI.get_room_alias` to `ClientAPI.resolve_room_alias`.