Infer Python package metadata from egg-info
When documenting a Python package, it would be helpful if Sphinx was able to extract package metadata such as the project name, author and version from the egg metadata. This could be done using pkginfo. I'm not sure whether an explicit switch should be provided to turn metadata inference on, or whether it would be sufficient to always try. In any case, inferred metadata should be overridden by the corresponding existing variables if these are explicitly specified.