It seems [libmill.org](http://libmill.org/) expired and got parked some time ago, and libmill's homepage is inaccessible even through the [github.io domain](https://sustrik.github.io/libmill). I think if you deleted the [CNAME file](https://github.com/sustrik/libmill/blob/gh-pages/CNAME) in the gh-pages branch then https://sustrik.github.io/libmill would work?
It seems libmill.org expired and got parked some time ago, and libmill's homepage is inaccessible even through the github.io domain. I think if you deleted the CNAME file in the gh-pages branch then https://sustrik.github.io/libmill would work?