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.
Maybe add a link to Engel's docs as well: https://github.com/basho/riak_ensemble/blob/develop/doc/Readme.md
Not sure we want to link that for operators or just devs