Stricter CMake flag behaviour
I would like CMake to fail the configuration step, if I provide flags such as
ELSA_BUILD_PYTHON_BINDINGS and the necessary dependencies can't be found. I would keep the default behaviour of turning on, if nothing is specified and the requirements are fulfilled.
I would introduce new options like
GENERATE_PYTHON_BINDINGS, turn the "old" ones internal only and if the new options are set to on, we force strict behaviour and if they are not set by the user, we fall back to the usual behaviour.