* New method skip(int) added to AbstractObjectIterator

* New constructor in RankingQueryOperation that accepts a collection (so no need to call setAnswerCollection)
* New query: JoinQueryOperation
* Serialization incompatible changes:
** New class DistanceRankedSortedCollection was added (it is generic and needs a DistanceRankedObject)
** RankedSortedCollection is now a descendant of DistanceRankedSortedCollection (formerly it was SortedCollection)