Feature/require cmake 3.1

Maybe we want to require CMake 3.5, not sure.

The failure is Debian 8 which does only provide CMake 3.0 out of the box.

So drop Debian 8 from testing?

I would also suggest jumping to 3.5 btw.

added 4 commits

• 4c95e4ca...1a82bde2 - 2 commits from branch master
• 5c6d3e2d - Require CMake 3.1
• bcf85fe4 - [CMake] Drop backported code from CMake 3.1

Compare with previous version

merged

mentioned in commit a9e49471

Yes, please drop Debian 8 for master.
I postpone requiring CMake 3.5. Let's see the reactions for CMake 3.1 first.

We should drop debian 8 now to fix the broken CI; either manually or by merging !320 (merged).

mentioned in issue #109 (closed)