JSON session file

Scheme layer used: 66

This version is primarily for people to migrate their .session files, which are pickled, to the new JSON format. Although slightly slower, and a bit more vulnerable since it's plain text, it's a lot more resistant to upgrades.

Please upgrade to this version before any higher one if you've used Telethon ≤ v0.10. If you happen to upgrade to an higher version, that's okay, but you will have to manually delete the *.session file, and logout from that session from an official client.

Other highlights:

• New .get_me() function to get the current user.
• .is_user_authorized() is now more reliable.
• New nice button to copy the from telethon.tl.xxx.yyy import Yyy on the online documentation.
• Everything on the documentation is now, theoretically, sorted alphabetically.
• More error codes added to the errors file.
• No second thread is spawned unless one or more update handlers are added.