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
Same as previous script, please add the three "set" commands to make sure errors do not go unnoticed.

If you really want the script to fallthrough even if a command fails, then add `|| :` or the equivalent `|| true` to the end of the line so that the `errexit` does not abort the script.