Cqlengine

* better logging for operational errors

* fix for connection failover

* fix for models not exactly matching schema

* support for table polymorphism
* var int type

* refactoring query class to make defining custom model instantiation logic easier

* added counter columns
* added support for compaction settings at the model level
* deprecated delete_table in favor of drop_table
* deprecated create_table in favor of sync_table
* added support for custom QuerySets