replace main.go with a bash script

[bacongobbler]

All main.go literally does is set a few environment variables and execute the registry binary as a child process. It would greatly simplify the build toolchain if we just made it as a bash script, especially with the introduction of #73.

[mboersma]

This didn't seem like much of a priority, and we can imagine wanting to add more functionality to it, in which case we'd be glad we implemented it in Go.