Change KV.Bucket to KV.Registry (elixir-lang#1044)

Author: dcadenas

getting-started/mix-otp/dynamic-supervisor.markdown

@@ -154,7 +154,7 @@ One flaw that shows up right away is the ordering issue. Since `KV.Registry` inv
 
 The second flaw is related to the supervision strategy. If `KV.Registry` dies, all information linking `KV.Bucket` names to bucket processes is lost. Therefore the `KV.BucketSupervisor` and all children must terminate too - otherwise we will have orphan processes.
 
-In light of this observation, we should consider moving to another supervision strategy. The two other candidates are `:one_for_all` and `:rest_for_one`. A supervisor using the `:rest_for_one` will kill and restart child processes which were started *after* the crashed child. In this case, we would want `KV.BucketSupervisor` to terminate if `KV.Bucket` terminates. This would require the bucket supervisor to be placed after the registry. Which violates the ordering constraints we have established two paragraphs above.
+In light of this observation, we should consider moving to another supervision strategy. The two other candidates are `:one_for_all` and `:rest_for_one`. A supervisor using the `:rest_for_one` will kill and restart child processes which were started *after* the crashed child. In this case, we would want `KV.BucketSupervisor` to terminate if `KV.Registry` terminates. This would require the bucket supervisor to be placed after the registry. Which violates the ordering constraints we have established two paragraphs above.
 
 So our last option is to go all in and pick the `:one_for_all` strategy: the supervisor will kill and restart all of its children processes whenever any one of them dies. This is a completely reasonable approach for our application, since the registry can't work without the bucket supervisor, and the bucket supervisor should terminate without the registry. Let's reimplement `init/1` in `KV.Supervisor` to encode those properties: