Bug#1053445: Merge request regarding 'Please migrate Release Notes to reStructuredText'

Hi Holger,

I really like the idea no to produce release notes for each
architecture but only one. Moving to sphinx is also nice.

Sorry, if I broke your MR, by adding code that checks if something
changed in the git repo. I think I can easily add this to your code
later. So maybe we copy your version of 7release-notes and after that
I add my code.

Do you know how long the build process takes using sphinx? I've added
the code, because the build took around 90 minutes using docbook.

Any other things I should keep an eye on?