Rewrite of the Guestbook example in Go

This is a Go version of the Guestbook example. The readme has been ported over from the existing one.

#1271
I'm setting `release.sh` to start from a clean state, and most of the time it is going to print ignorable errors if it is not suppressed. I'm not doing this in the `clean.sh` script itself because when you run it explicitly you should be able to see what the script did or didn't do.