python-paramiko: Update and clean up meta.

The upstream package has a new maintainer (Jeff Forcier) and thus the
main homepage for the project is the GitHub page.

Also the long description contains quite a lot of unrelevant
information, so I've used the one from PyPI, which is a lot smaller and
just contains what the library supports and does.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>