Remove RPATH from build flags. It's not needed on Linux and may cause maintenance problems. See: https://wiki.debian.org/RpathIssue ===================================================================
Install to correct site-packages dir, based on Python version. The Debian hack in CMakeLists was removed upstream, but python3 doesn't report a Python-specific site-packages folder. This is required, because SIP packages need to be compiled and installed for every Python version separately. ===================================================================
