Sentinel support

[okharitonova]

Added sentinel support. Returns master/slave connection via master name.
Choice of slave supports round-robin balancer.
Example of use:

sentinel = await Sentinel.connect(host='localhost', port=6379)

master = await sentinel.master('mymaster')
data = await master.hgetall('key')

slave = await sentinel.slave('mymaster')
data = await slave.hgetall('key')

[danigosa]

Any news into integrate this to master and bump version?

[dikderoy]

btw, I am working on a full featured sentinel support in separate package (built on top of this one), with backoff-support and also planning to add preemptive connection reconfiguration (via listening of sentinel events) - if any one interested - here is a link

[jonathansp]

Any news here?