Ready: Strong consistency update

- [x] Configs in `advanced.config`
- [x] `riak-admin` interface for ensemble
- [x] Implementation details

Heads up to @andrewjstone, @engelsanchez, and @jtuple when he's back.
The following two sections imply that you need at least 3 nodes before making any changes to riak.conf. I'd change the wording to separate the enabling of individual nodes in the config file from the activation that occurs once 3 enabled nodes are detected by riak.