Refactoring: Split fonts.nix into smaller modules
fontconfig: Set the default hinting style to "slight"

This works around a bug in infinality that causes broken rendering in
some cases.  Issue NixOS/nixpkgs#663.

Upstream suggests that "slight" is a better/safer default in any case.
It also looks better, IMHO, YMMV.
Updated disnix to latest 0.3 release
info program: use latest texinfo