Calls for Telethon

This module aims to provide support for performing voice calls through Telethon <https://github.com/LonamiWebs/Telethon>_. Please note that currently this module is far from usable, and is more a proof of concept.

Huge thanks to @stek29 <https://github.com/stek29>_ for his amazing gist <https://gist.github.com/stek29/9ced63a52199faf2d0b2fd9e99b49109>_ on how to get calls working, and for helping me spot certain bugs that occured after porting the JavaScript code to Python. Thank you from saving me from another three days of headaches!