This release lets the filestore work with raw multihashes directly rather than
CIDs.

In the context of usage within go-ipfs, the go-filestore module should have
always worked with blocks addressed with CIDv1s of type Raw, which map to raw
multihashes, and therefore requires no migration in the underlying storage.

However, as a public module with a public interface, we tag v1.0.0 to avoid
unintended breakage through minor-version upgrades to potential third parties
which may have, for some reason, used it differently or used it wrong, even if
chances of this happening are slim.