Non-Printable Character Detection

Replace non-printable characters, e.g., zero-width spaces, with a visible symbol.

Verzia zo dňa 16.09.2021. Pozri najnovšiu verziu.

Replace non-printable characters, e.g., zero-width spaces, with a visible symbol ❖.

I only included control characters (\p{Cf}) mentioned in https://stackoverflow.com/a/12054775/8056404.