feat: support Peer ID represented as CID

[lidel]

Motivation

This PR implements Stage 1: Parse CIDs as peer ID from https://github.com/libp2p/specs/issues/216.

TL;DR This PR does not change the default text representation of Peer IDs, all we do in Stage 1 is adding support for creating PeerId objects from CIDs.

For a wider context see libp2p/specs/RFC/0001-text-peerid-cid.md, short story is that CID support will enable IPFS project to support /ipns/{cid} in Base32 (https://github.com/ipfs/ipfs/issues/337), enabling things like http://{libp2p-key-as-cidv1b32}.ipns.dweb.link

Changes

This PR adds two functions:

• createFromCID accepts CID as String|CID|Buffer and creates PeerId from the multihash value inside of it
• toCIDString serializes PeerId multihash into a CIDv1 in Base32 (libp2p RFC 0001)

Next

• We need this released and bubbled up, so we can switch IPNS implementation in js-ipfs to createFromCID in https://github.com/ipfs/js-ipfs/pull/2566

cc https://github.com/ipfs/ipfs/issues/337, https://github.com/libp2p/specs/issues/216, https://github.com/libp2p/specs/pull/209, https://github.com/ipfs/go-ipfs/issues/5287

[lidel]

ping @vasco-santos

[vasco-santos]

@alanshaw any other feedback that you want to provide here? I think we can go with this