Multistream Version Handling

[whyrusleeping]

we need to change our multistream protocol id's to match what is expected by js-ipfs. In order to do that, we have proposed changing the multistream interface to expose the selected version on the stream object passed to the handler so that protocols will be able to detect which version they are communicating over and behave accordingly.

related:

• signal selected protocol to callers multiformats/go-multistream#7

[whyrusleeping]

There is also the problem of knowing which protocol to dial to for a new peer. Trying both at the same time is wasteful, trying one and then the other increases latency. I propose that we start using the protocols field of the identify handshake to seed the peerstore with info on what protocols are supported by each peer we connect to.