You can't see it from here, but go-mulithash now uses registry system,
so it's reasonably possible to introduce new hashers, and to use
(some parts of!) go-multihash without bringing in lots of transitive
dependencies.
The main package of go-multihash still brings in everything
transitively that it did before, so go-cid's transitives aren't
shrinking, and no code is changing here... but it's closer.
If we did cut over to the new go-mulithash/core, we could make
many transitive dependencies become optional.
