* make font derivations fixed-output where applicable
* fix dead links
* `stdenv.lib` -> `lib` where `stdenv` is not involved
* remove `meta.platforms = [ unix ]` and `meta.platforms = [ linux ]` because the restriction has no sense for data packages
It is a bit unfortunate that the name is so close to material-icons,
however it is consistent with the project name and how it is present
in AUR (ttf-material-design-icons-git)
