v0.21.0

• (event) Added support for creator power in room v12+.
• (crypto) Added support for generating and using recovery keys for verifying the active device.
• (bridge) Added config option for self-signing bot device.
• (bridge) Removed check for login flows when using MSC4190 (thanks to @meson800 in #178).
• (client) Changed set_displayname and set_avatar_url to avoid setting empty strings if the value is already unset (thanks to @frebib in #171).