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.
`build` technically is `install`, since it really just does `go get` (where `go-wrapper get` is really `go get -d`, ie, download only)