DATAREDIS-313 - Overhaul SCAN, HSCAN, SSCAN, ZSCAN operations.

Unify naming and return types. Update supported commands documentation. Remove key from BoundHashOperations and use getKey() instead.

Original pull request: #81.
DATAREDIS-313 - Overhaul SCAN, HSCAN, SSCAN, ZSCAN operations.

Unify naming and return types.
Update supported commands documentation.
Remove key from BoundHashOperations and use getKey() instead.
Prevent error when trying to read values when there are no values present.