Create a proxy server using cloudcfg.  Useful for demos

you could consider having a function e typthat return an error and implement `ServeHTTP` like this:
https://github.com/GoogleCloudPlatform/appengine-goshorten/blob/master/goshorten.go#L70
https://github.com/GoogleCloudPlatform/appengine-goshorten/blob/master/goshorten.go#L70