fix: missing id name constant

[vasco-santos]

As go specifies the multihash ID constant, we should do the same here.

It is used for libp2p-id, and consequently for IPNS

[achingbrain]

Weirdly now this module exports a hash name that it can't use to hash a buffer after this change. Not sure if that was intentional:

const mh = require("multihashes")
const names = Object.keys(mh.names)

mh.encode(Buffer.from([0, 1, 2, 3]), names[0]) //  Error: Unrecognized hash function named: id

Just discovered this because the ipfs-unixfs-engine module arbitrarily use the first 40 hashes exported by this module in some of it's tests.

Also, since this is for go compatibility, id should be added to the codes and defaultLengths objects too since go does here and here.

[vasco-santos]

Hello @achingbrain , sorry for the late answer

IPNS needs to verify if a multihash represents an ID. This way, it was added as a multihash name, the same way as go does. And yes, I agree that it should be added to the codes and defaultLengths. I can create a new PR adding them.

Regarding the ipfs-unixfs-engine, I believe that the name constants have the purpose of identifying types of multihashes, and consequently, not only hash algorithms. So, I think that we should obtain a set of hashing algorithms in a different fashion for those tests. What do you think?