OperatingSystem implementation for Linux

[be4zad]

It seems operating system name is same with distro name.
Isn't it better to remove GeneralReadout::distribution() and replace it by GeneralReadout::os_name()?

[be4zad]

behzad@arch ~> hostnamectl
Operating System: Arch Linux 
…

[grtcdr]

I made that distinction in the API to accommodate the differences in semantics between operating systems. Operating systems built on Linux refer to themselves as distributions and the API reflects that, whether that was the right choice is debatable. I just don't think it's worth breaking backwards-compatibility for such a minor problem.