Specify the target required c++ version

[jmigual]

Without this, the user importing the library is forced to set:

set(CMAKE_CXX_EXTENSIONS OFF)
set(CMAKE_CXX_STANDARD 17)

somewhere in their project. With this, the library can be just linked with:

target_link_libraries(<my_target> maxplus)

and the right c++ version is already set.

[jmigual]

@MarcG-TUE

[MarcG-TUE]

I did see it, but I haven't had time to fix the mess caused by the TU/e enterprise thingy...
when I tried I was not allowed to merge.

[jmigual]

Ah, I see. I still cannot see the TU/e enterprise organisation on GitHub. :/