Prep for pypi release

- Change project name to `google-apitools` to avoid conflict with existing PyPI project.
- Drop obsolete `provides` metadata.
- Move README to ReStructuredText, in order to include it as the `long_description` on PyPI.
That would be more precise:  I updated it in d143231.  The `google_apitools` spelling works because distutils normalizes hyphens to underscores under the covers.