Hey @rvagg,

With this as the "canonical" dagpb implementation, I'd like to look at replacing go-ipld-prime-proto. At the moment, there are some elements missing that prevent me from doing this:

1. go-codec-dagpb appears to lack support for RAW nodes as leaves a UnixFS dagpb tree structure -- this is immediately essential for Filecoin which uses raw leaves whenever it generates IPLD UnixFS V1 DAGs. I'm not sure that this makes sense as part of this library -- or alternatively as a seperate codec (dag-raw is not an actual format, but bytes as leaves of the dag is part of UnixFS v1, and it's relatively trivial to implement the loading part of this at least so that the bytes are read to a Bytes node). Maybe this should just wait for flexible byte layouts and other ADLs?
2. go-coded-dagpb uses refmt for protobuf deserialization/serialization, while go-ipld-prime-proto uses the same code-gen'd serializers used by go-ipfs (see go-merkledag). I have two concerns about switching to refmt:
   1. I need to verify performance is comparable
   2. I need to verify refmt is 100% compatible with the generated serializers/deserializers in go-ipfs

Anyway, I am going to go ahead and update go-ipld-prime-proto to go-ipld-prime v0.7.0, but I'm hoping to work with you so that's the last update. I'd be happy to go over all the features of go-ipld-prime-proto and how they are used so we can figure out how to swap out the libraries for go-graphsync.