Change getchef.com to chef.io

:convenience_store: 

This is mostly ready to go.  The one glaring omission here is the VCR cassettes, but I think we need to wait until chef.io is live, and then re-run those specs.  The eminent @bcobb gave me a good idea of what needs to happen there.  That will likely happen in a subsequent PR to this one, unless someone else has a better idea.

I don't think we want to merge this until we're ready for the domain to be live.

Closes https://github.com/opscode/supermarket/issues/918