Currently the manual scales to the view port of the browser.
This leads to an unreadable layout and I found myself
reading the xml source instead.
The optimal width would be around 50 characters per line.
Since we have code listings also in the manual I relaxed
this limit a bit towards 70 characters per line.
- Rectifies diverging CSS by combining
nixos/nixpkgs docs CSS
- Moves our custom Highlight.js loader in to
the hljs package
- Switches the nixos docs to use SVG
callouts too
