Re-export libp2p_identity::PeerId?

[dav1do]

While updating a project with dependencies on multiaddr and multihash, I noticed that libp2p_identity::PeerId isn't re-exported but is in two public interfaces: MultiAddr::with_p2p and Protocol::P2p. Any objections to a re-export (or a wrapper tuple struct with Deref/DerefMut)? I'm happy to make a PR, but I figured I'd ask first as it has dependency/API ramifications.

I know the libp2p-identity crate is small so I could add it, but it'd be nice to have this library be self contained. I have an API that looks like a tiny bit of IPFS, which is why I want address info without actually pulling in libp2p proper.

[thomaseizinger]

A re-export of PeerId seems fine to me, yes :)