Remove costly 'appendIfNotExists' and 'remove' call from PubSub (redi…

…s#743)

* remove costly 'appendIfNotExists' and 'remove' call from pubsub

Merge pull request redis#742 from go-redis/fix/with-context-wrap-process

Fix WithContext followed by WrapProcess

Merge pull request redis#737 from gbbr/context

cluster: add support for context.Context to ClusterClient and Ring

Fix doc

Fix proto.RedisError in slices

Rework retrying

Add WrapProcessPipeline

Merge pull request redis#696 from go-redis/fix/cluster-closed-node

Retry if node is closed; close nodes with delay

Remove StringToBytes

Merge pull request redis#688 from go-redis/fix/random-node

Pick random node when command does not have keys