Zero downtime deploy

[bakwc]

Documentation is here.

• Added versions to replicated decorator: @replicated(ver=2)
• Added ability to switch cluster-version

[coveralls]

Coverage decreased (-0.08%) to 88.551% when pulling 0c98414 on zero_deploy into 17c2f1d on master.

[coveralls]

Coverage decreased (-0.8%) to 87.825% when pulling 4009f5a on zero_deploy into 17c2f1d on master.

[coveralls]

Coverage decreased (-1.09%) to 87.544% when pulling a3c438a on zero_deploy into 17c2f1d on master.

[coveralls]

Coverage decreased (-1.08%) to 87.555% when pulling fa9d319 on zero_deploy into 17c2f1d on master.

[coveralls]

Coverage decreased (-1.1%) to 87.511% when pulling 0c09ee9 on zero_deploy into 17c2f1d on master.

[coveralls]

Coverage decreased (-1.1%) to 87.511% when pulling 0905e79 on zero_deploy into 17c2f1d on master.

[coveralls]

Coverage decreased (-0.9%) to 87.745% when pulling 62e800c on zero_deploy into 17c2f1d on master.

[coveralls]

Coverage decreased (-0.1%) to 88.53% when pulling 25ce9c0 on zero_deploy into 17c2f1d on master.

[coveralls]

Coverage decreased (-0.02%) to 88.618% when pulling 4970cbd on zero_deploy into 17c2f1d on master.