Bridge Telegram call events to Matrix as messages

[MurzNN]

I use Matrix as main Telegram client, so Telegram app is frozen via IceBox app most of time, and unfreeze native Telegram app only for make/receive calls. And when someone try to call me when app is frozen, I see no incoming events on devices, because call events are not bridged to Matrix. So, I totally miss incoming call until user write me text message "Why you don't answer to call??".

Before implementing #103, is this possible via Telethon library to intercept Telegram incoming call events and post it in Matrix room as messages? If not for incoming calls, maybe at least for missed calls?