Add simple "go-wrapper" script for building and running, especially to accommodate ".godir" support

Fixes #4
Fixes #9

Also, `update.sh` will make sure it's properly copied into each version subfolder, like we've done with other official images.
It basically amounts to `go get -v -d && go build -v && go install` right now, where `go-wrapper get` amounts to `go get -v -d`.