Add `target_compile_feature` command to `CMakeLists.txt`

[ghost]

This commands pass required C++14 standard flag to compiler.

[sasq64]

C++14 is set using a global property at the top of the CMakeLists.txt so I don't see a need for it to be set for each target ?

[ghost]

The target_compile_features pass -std=c++14 to compiler.

And the doc of CXX_STANDARD_REQUIRED says:

For compilers that have no notion of a standard level, such as MSVC, this has no effect.

[sasq64]

Is this a real problem for MSVC ? I don't see anything in the documentation that implies CMAKE_CXX_STANDARD is weaker than target_compile_features(cxx_std_) and I prefer to apply possibly ABI breaking stuff globally.