correctly parse custom configuration with nested HTML comments

[JeanMertz]

While investigating https://github.com/rustic-games/jilu/issues/13, I noticed that the default template has nested HTML comments at line 68 and 84.

This causes the config parser to break If you copy this template verbatim into your CHANGELOG.md.

The parser should handle nested HTML comments by counting open/close comment markers, and only stop parsing once the root marker is closed.