[Catalog-sig] PyPI trove classifiers for alternate language implementations

["Martin v. Löwis"]

> Programming Language :: Python :: Implementation :: CPython
> Programming Language :: Python :: Implementation :: PyPy
> Programming Language :: Python :: Implementation :: Jython
> Programming Language :: Python :: Implementation :: IronPython
> Programming Language :: Python :: Implementation :: Stackless

I have now added these. To support this structure, the slightly bogus
"Programming Language :: Python :: Implementation" classifier needed
to be added as well.

Regards,
Martin