adding blake3 support, bumping versions

[laudiacay]

adding blake3 stuff and bumping multihash version. bumping minor version here too.

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[laudiacay]

depends on this getting merged: multiformats/go-multihash#158

[Jorropo]

Golang's dependency model is not tree like.

Except counting /v2, /v3, ... branches (which we are not using here). Only one version of the package is compiled (the latest one).

If a consumer (like go-ipfs) updates to a later go-multihash this also updates it for all other users of this module (like go-cid).

I think this can be closed, if someone need some custom go-multihash for some blake3 thing they can just update to the newer go-multihash.

[laudiacay]

phew one less to worry about.... so i guess we just need to bump go-verifcid on go-ipfs, and get the go-multihash bugfix in.