title: Riak max-counter
body: <p>I'd like to implement sth like a max-counter using Riak's CRDTs to use w/ Yokozuna.
  The idea I had was to have a Riak map, two counters inside it, one to be modified, then the other to be updated to the max of both in a pre-commit hook.
  However, I can't seem to find a way to update a Riak map to do just that.
  Any help/better idea?</p>