Back button for Picklist

• PickOptBtnBack - automatically adds a back button with text generated by textFn function argument.
• PickOptBtnBackWithText - convenience function, to declutter the option call if the caller doesn't need to worry about i18n

Upgrade for Telebot.v3

This release is tailored for the version 3 of the telebot library.

• All handlers updated to support telebot.Context.
• Convenience logging function SenderInfo that gets the user from the telebot.Context.
• Boter and other auxillary interfaces are removed, as the bot instance can be retrieved from the telebot.Context.

Public release

v0.2.1

public release (unstable)