Merge pull request redis#443 from go-redis/fix/cluster-nil-ptr

Fix nil ptr in case when all nodes are unavailable.

Merge pull request redis#434 from go-redis/fix/timeouts

Set read/write timeouts more consistently.

Merge pull request redis#431 from go-redis/fix/instrum-example

Fix WrapProcess for Ring and Cluster. Add better example.

Merge pull request redis#418 from go-redis/fix/limit-alloc

Limit allocation.

Merge pull request redis#416 from go-redis/fix/cluster-state

Use consistent cluster state when executing pipeline.

Merge pull request redis#409 from bpiddubnyi/bugfix/setxx-zero-ex

Fix "invalid expire time in set" for SetXX with expiration = 0

Update changelog.

Merge pull request redis#398 from yzprofile/v4

fix broken cmdable interface of redis.Tx

Merge pull request redis#405 from go-redis/fix/lowercase-name

Lowercase command name. Updates redis#399.

Merge pull request redis#385 from go-redis/fix/enable-reaper-and-add-…

…tests

Enable reaper on ClusterClient and add tests.