Bitswap spec update

[dgrisham]

Editing and updating the Bitswap spec. Work in progress. Starts from #168

[dgrisham]

@diasdavid This is ready for a first-pass review :)

[daviddias]

Skimmed through it, so far so good :)

[daviddias]

@dgrisham when will the final version be ready?

[dgrisham]

I'll work on getting the Bitswap sessions section together within the next week or so when I have time. That and the API are the most substantial parts left -- is the API far enough along to be set, or should that be left unfinished for now in lieu of future changes?

[Stebalien]

If possible, let's try to keep the pieces separate. There are three parts:

1. The network protocol. This is the "real" spec, the description of how nodes work together.
2. Concepts/algorithms (e.g., sessions). Nodes should follow these guidelines but, really, these are just suggestions on how to use the bitswap protocol effectively.
3. Service API. Is that even part of the spec? I guess it's useful as a "and here's what bitswap is for"...

[daviddias]

sounds good @dgrisham. Let's take it as it is and continue from there.