Fix C++ version requirement mismatch between the CmakeLists and the code

[jeanchristopheruel]

'auto' type appears several times in the code, requiring the compiler to support at least C++17.

However, the CmakeLists suggest a minimum requirement for C++11.

It was initially planned to limit the C++ version dep to C++11 in order to reach a broader audience.

Refer to #19

[jeanchristopheruel]

Addressed in #22 , I chose to upgrade the build requirement for C++17. It simply allow to make cleaner code.