The shared in-memory key-value store, a single GenServer backing every endpoint.

It holds two independent keyspaces so both the bucketed and bucketless protocols can share one process:

• a bucketed space — put/3, get/2, delete/2 take (bucket, key) and are used by FakeRiak.Riak;
• a bucketless space — put/2, get/1, delete/1 take just (key) and are used by FakeRiak.Redis, FakeRiak.Etcd and FakeRiak.Memcached.

get replies {:ok, value} or {:error, reason}; put/delete reply :ok (with delete returning {:error, reason} when the key is absent). The public functions run in the caller's connection process, so when --verbose is set they log each operation, attributed to that connection's protocol.