Sentinel support

[freswa]

Thank you for creating this great tool! I'd like to connect to a redis sentinel set of hosts instead of a single instance as documented here.
I think the best approach would be to either add another option which takes a list of sentinel hosts or use the existing -s option and modify it's syntax by allowing e.g. url style args as sentinel://[user:pw]@sentinelhost:5000,anotherhost:5000.

What do you think?