Fix typo
Polish documentation
Provide Redis Sentinel connections using lettuce 3.x

Implement Sentinel support using lettuce library, adopt finer grained exceptions and aligned exception behavior to match other libraries. Added shutdown-timeout property in order to control shutdown duration of the netty framework which reduces test run duration. Documentation updated as well. Contains also a fix to use psetex instead of setex (typo).

Reference: DATAREDIS-348