package: some additions to setup.py and docs conf

- Module nix.info defines author, version, contact etc.
- Use nix.info in setup.py
- Additional definitions in setup.py such as descriptio and classifiers
- Use nix.info in docs/sources/conf.py
setup.py: use pkg-config for compiler flags
setup.py: set version to 0.9.2
setup.py: parse info from nix/info.py
info.py: set version to 0.9.3