Adjust dependencies of core archive for allowing builds
for python modules and build for executables when -DPYBIND=ON.
Build can now be performed with -DPYBIND=ON and -DTEST=ON.
Build can be done in case where the python libraries are not
present (cibuildwheel), though in this case it is not possible
to build standalone executables.
Install pybind11 headers as part of interface in order to
provide complete dependencies.
Add AIDGE_BUILD_TEST envvar to setup.py to -DTEST=ON.
Update required cmake version which should be actually >=3.18.
Update and fix README.

Co-authored-by: Grégoire Kubler <gregoire.kubler@proton.me>