fix a bug in fetch that cause duplicate joined key (maybe co-group is better in bijectory case)
fix a bug in slice that cause duplicate newPages not removed.
all syntax sugers of PageRowRDD (functions start with visit & wget) now have only 1 pair of parenthesis.
Add ExplorePagination integration test
correct keyDelimiter in a unit test
change some Visit in integration test ot Wget for diversity