Use CMake

[stellarpower]

It'd be much nicer if we could use CMake, rather than invoking the compiler directly in the setup file - sure everyone will agree that this seems a guaranteed cause of issues in a larger project, or if other libraries need to be used.

Pybind11 has a nice CMake example here, I think it would be sensible to make some changes so that this example could make use of what they have there.

Otherwise, have to commend you on how easy this was to set up in a short space of time.

Cheers!