ISPN-4966 The <backups/> element should be a sub-element of all cache-types, not just clustered caches
Update locking documentation

* added how it works in clustered caches
ISPN-4970 AvailabilityException and AvailabilityMode are in the wrong package
ISPN-4970 AvailabilityException and AvailabilityMode are in the wrong package

Move the impl package as well
ISPN-4981 Update to Hibernate Search 5.0.0.Beta2
ISPN-4981 Spatial Query updated API: onCoordinates -> onField
ISPN-4902 Unsupported Class Version Error when running testsuite with JDK6

Update documentation.
Configure event sender as an async Listener

* Ordering is only guaranteed as long as the async listener executor
is configured with 1 thread, which is the default.
* By using async listener, construction of the event and sending it
is taken out of the critical path of the Hot Rod client request.