Draft changes for sharding cacheops

Hi, Alexander!

It seems I have got working version of sharded cacheops. I changed a lock behavior for compatibility with `twemproxy`. After that I assembled scheme with twemproxy and two redis servers behind it. And it works perfectly. Of course, I did not test it with high  concurrency and high load yet. I plan to check my changes on test stage and production after vacation.

But now I would be happy if you will check my changes and discuss it with me.

I see some narrow places in the new behavior. Like `max lock time`. But there are some improvements. For instance, lock became more granular.

Also versions of server and client must be increased. Server >= 2.6.12, client >= 2.7.4

You can see my twemproxy config (YAML)

	redis1:
	  listen: 192.168.144.170:6379
	  redis: true
	  hash: fnv1a_64
	  distribution: ketama
	  auto_eject_hosts: true
	  timeout: 400
	  server_retry_timeout: 2000
	  server_failure_limit: 1
	  servers:
	   - 192.168.144.151:6379:1
	   - 192.168.144.61:6379:1


Thanks in advance!