code: function Recorder (paxos) {
      var entry = paxos.log.head.body
      this.register = {
          body: {
              promise: entry.promise,
              body: entry.body,
              previous: entry.previous
          },
          previous: null
      }
      this._paxos = paxos
  }
docs: TODO Remember that the code is more complicated than the messaging. Let the messages absorb some of the complexity of the code. (Divide them. Restrict their structure.)