Fix version in the Python package metadata
    
    The version was 4.0.0-unsupported which is both incorrect data
    and invalid Python package version and will fail with python-packaging 22+.
    
    In the meantime, upstream made the fallback version valid:
    https://github.com/mkleehammer/pyodbc/commit/996fce118ee9fe6dc685a6bd8c25e80b270e250c
    But that does not help us provide correct metadata.
    
    The logic in setup.py tries to use `git describe` (which fails because there is no git repo)
    or to parse PKG-INFO from sdist (which fails because this package does not build from sdist)
    to get the version.
    
    Creating a stub PKG-INFO file with just the version appears to work fine.
    To make sure it keeps working with future versions of pyodbc,
    the %files section was made much more explicit,
    which is required by the Python package guidelines (to some extent) anyway.