add go-car impl url

[daviddias]

@whyrusleeping can you give a pass through the spec and see if it matches your implementation and update if needed?

[whyrusleeping]

@diasdavid no, this does not match my impl. This is not a spec, it is a draft, and was never finalized (why is it merged?)

cc @Stebalien

[whyrusleeping]

Ah, you merged it @diasdavid. See comments here: #51 (comment)

[Stebalien]

Yeah, @whyrusleeping's impl is just tar. Not the best solution but it works, exists, and very much doesn't suffer from NIH.

[daviddias]

Got it. Added the label WIP to it. d2f7b50

[rvagg]

The CAR spec was removed in #72 so this is no longer a valid PR so I'm closing this. However, I think we might need to bring it back since it's in active use for Filecoin genesis. I've also created a ZIP CAR that's very similar but conforms to the Datastore interface and I have implementations in both JavaScript and Go, mainly for cross-language test fixtures, but I might spec that up too.