Header generation is triggered every time "setup.py" is called

The fix for issue #11 (closed) introduced additional text output to the console when running the setup.py with any subcommand.

$ python3 setup.py --name
installing C++ header file -> lisaconstants.hpp
installing C header file -> lisaconstants.h
lisaconstants
$ python3 setup.py --version
installing C++ header file -> lisaconstants.hpp
installing C header file -> lisaconstants.h
1.0.1

The installation of header files should only be done on install, IMO. Or even with an explicit subcommand like install_headers, but not always. This additional text output might break some CI scripts, that extract the version number that way.