[Dune] Possible release notes for 2.1.1

[Christoph Grüninger]

Hi Oliver,
my patch is aligned with older release notes. For example Dune 1.1.1 
introduced little more than g++ 4.3 compatibility but has it's own page 
to document the changes.

> That way we avoid a proliferation of small
> pages and corresponding entries in the navigation bar.

There won't be any new entry in the navigation bar, it will be replaced.
Though it would be a good idea to introduce a folder for the old release 
notes.

Why should we change the way release notes are handled?
Continuity is a virtue of bureaucracy.

Have a nice day,
Christoph