Log wrapper

[bailantaotao]

Hi, I used the Redis Pub/Sub to serve each HTTP request channel, but I can't figure out which IP is getting the channel is full error. Because log is global in Go-Redis.

I propose an idea where users can pass a log ChannelOption in PubSub.Channel so they can detect which one had an error occur.

Please~~

[ycdesu]

It's really a useful feature. Hope the pull request can be reviewed

[ndyakov]

Let's spend some time on designing a better logging, we are open to proposals to decide which interface the logger should follow.