Remove references to carbonzipper

Hi,

I have seen in several documentations that `carbonzipper` is included in `carbonapi` and not needed anymore since version 0.8.

So could the cluster graph be adjusted to remove the `carbonzipper` block?

Maybe also update the link to `carbonzipper` on the README file to https://github.com/go-graphite/carbonapi/tree/master/cmd/carbonzipper ?