Merge pull request #29 from dukhlov/master

Put request schema added
Cassandra backend: update item
Conditional updates are not supported
'Add' operation is not supported
Cassandra backend: put item
Conditional updates are not supported
Put method implemented
Merge pull request #30 from ikhudoshyn/cassandra-update-item

Cassandra backend: update item
Merge pull request #2 from Mirantis/master

update local fork