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and rebuild protobuf file

Use proto2 syntax

gossipsub

Add a spec link for gossipsub

Add and update info on gossipsub and implementations

so that travis doesn't get killed by OOM.

it is really testing full queues (sized 32) and retries of control
messages and announces

don't create a control object if the graft/prune are stale and only assign
the relevant fields.

they are very important for correct topic state in the protocol, esp gossipsub

- the check is unnecessary because peers emit PRUNE on Leave
- the check is harmful, because the ANNOUNCE message might have
  benn lost (or reordered after the GRAFT depending on the retry
  strategy), which would leave the mesh in an inconsistent state.