Update of the build system

- The results of C++ feature detection are now cached.
- The results of GL extension detection are now cached.
- Reorganized the cmake scripts.
- Added generation of a python script that contains info about
  the configuration of the current machine.
- The configure.py's --gl-header-lib option was renamed to --gl-api-lib.
- Added a utility script for testing if all available configurations
  build properly.