feat: add default error handler

[jrriehl]

• Renames misnamed _handle_error function to _send_error_message
• Adds a default error handler that can easily be overwritten if desired

A possible bonus is that rather than an empty protocol being default, the default protocol will now have something in it.

[Archento]

Apart from my one question this works perfectly as intended. Overwrite/rewrite of the internal handler is also easily possible.
Very happy with the quick solution :)