Add sub-version output to version command

[kofalt]

It would be nicer if hroot version made it clear that a build came from development after a version release. I've seen docker and other projects do this, adding this feature would make binaries less ambiguous.

However, the build script should not fail if the git command or .git folder is missing. We have two build deps, go-1.2 and bash; let's keep it that way.