conversions were done using https://github.com/pennae/nix-doc-munge
using (probably) rev f34e145 running
nix-doc-munge nixos/**/*.nix
nix-doc-munge --import nixos/**/*.nix
the tool ensures that only changes that could affect the generated
manual *but don't* are committed, other changes require manual review
and are discarded.
https://humdi.net/vnstat/CHANGES
* enable tests
* add hardening options from upstream's
example service
* fix "documentation" setting in service:
either needs to be `unitConfig.Documentation`
(uppercase) or lowercase but not within unitConfig.