Add a hash package.

This is for juju backups.
Also, in Go I've found that at most meaningful scales it's better to split a file into several smaller files along the group boundaries than to use comments as dividers.  This often extends to creating a new package for the once-a-single-file.  However, splitting up a file is not always practical, particularly when creating a new package out of it would introduce too much risk (or churn).  Even then, though, I'd still argue it's worth it in the long run...if you can afford to eat the short-term cost.