No documentation on text editor

[MikkoWrightson]

The text editor has no documentation and it'd be really nice if it had at least a bit, it's a bit of a pain to always do everything via uploading files

[andrewlytvyn]

/**

• Implements a simple select-replace file editor in Telegram.
• It works as follows:
• 1. The user invokes the editor with a non-empty file.
• 2. The contents of the file are posted as a message.
• 3. The user replies to that message with (part of) the text.

• The bot will locate that substring in the file contents and track the message.
  

• 4. The user edits his message.

• The bot will then replace the original substring, save the file and edit its message.
  

• If there are any problems with saving the file, the editor may detach.
  

• NOTE: sync I/O is used for simplicity; be careful! (TODO)
  **/