Changelog for ppad-pbkdf-0.2.0

# Changelog - 0.2.0 (2025-06-21) * The 'derive' function is now total, returning 'Nothing' when supplied with bad inputs. - 0.1.1 (2025-02-24) * Minor Haddock fixes. - 0.1.0 (2025-02-24) * Initial release, supporting a generic RFC2898 PBKDF2 function.