Feature: libp2p interop

[mkg20001]

See #84

Merging for now because otherwise this pr explodes with fixes needed in master

[danimesq]

Reference: #84.

[mkg20001]

Todos:

• [ ] do znv2 handshake
  • [ ] If peer.libp2p
    • [ ] do libp2p/multistream handshake and muxer, crypto, etc
    • [ ] create a conn with /zn/2 as client
    • [ ] store conn with client and with libp2p flag
  • [ ] else
    • [ ] store conn
  • [ ] if proto is /zn/2 or !proto
    • [ ] if !peer.libp2p
    • [ ] cb(null, client)
    • [ ] else
    • [ ] cb(null, conn.client)
  • [ ] else
    • [ ] if !peer.libp2p
      • [ ] fail with error "no libp2p support"
    • [ ] else
      • [ ] do hacky dial with proto