Update entry in Python Package Index

[mmdriley]

https://pypi.python.org/pypi/google-apputils/0.4.0

Need to at least update project URL to reflect change to GitHub.

[gpshead]

https://pypi.python.org/pypi/absl-py/ replaces this library. We need to update the full PyPI entry to direct people migrate their code to use that. For the time being I've updated the summary text to read "Obsolete. Please migrate to absl-py instead." as I could do that through the PyPI web interface.