Message Passing for Heterogeneous Paxos

[isheff]

This issue may well be combined with our existing ledger projects.

Ultimately, our Heterogeneous Paxos implementation will need to send messages (1b, 2a, etc).

• How do we format these?
• How do we disseminate them?
  • While Gossip is efficient in terms of per-node bandwidth and connections, just sending UDP packets to all destinations might be faster, although we'd have to be clever about filling in messages that some recipients missed.
• what, if any, signature aggregation do we use?
  • trees of signature aggregation have in the past been fruitfully combined with gossip trees.