PyPI package needs to have a bus factor higher than 1

[tommorris]

I propose to add Tantek Çelik (@tantek) as a co-owner of the PyPI package to ensure the bus factor higher than one.

The intention is to ensure that if I were to fall off the face of the planet, get hit by a bus, get invited to live on an internet-free commune (etc. etc.) there is someone to delegate a new maintainer of the PyPI project.

[tommorris]

@kevinmarks is a co-maintainer, so we've got bus-factor > 1 now.