Integrate conflux proposal into main specs

The documentation for conflux is still in proposal 329; it would be good if we had it merged into the specs instead.

This will probably take a little more than just copying the file; we should at the least double-check it for accuracy with respect to arti, remove any parts that we didn't implement, and integrate its various pieces with their corresponding pieces of the spec.

It might be a good idea to do this while the experience of implementing it in Arti is still fresh in people's minds.