Still some problems with GenericArray and byte. Seems fixed now
Added a macro that gets a repository digest

A repository digest is a unique digest representing
the contents of a repo. It is calculated by taking the
sha-1 of its contents, sorting them, removing duplicates
and then digesting them with sha-1. The macro
visits all repositories and any repo with a getDigest
method is added to the list.

jim can use this to calculate the dependencies.