Modify set rollups to track individual items seen instead of counters.

This is done by hashing each object as it observed, and storing the hashes.  hashes are then merged on rollup.

This puts SetRollup in the same class as TimerRollup in that full-resolution stores rollup objects rather than primitives.
Update README.md
introduce a 5ms gap into the time between when a thread starts and it starts running its runnable. This will make the test work the way it is expected.
Merge pull request #204 from gdusbabek/slow_batch_read_test

Fix testBatchGet() failures
Merge branch 'master' into set_rollups_v2
use getHashes() instead of accessing hash directly.
update changes
Merge pull request #203 from gdusbabek/set_rollups_v2

Set rollups v2 - track individual items across rollups (up to 24h)
Simplify slotFromFinerSlot computation
Fix NPE when updating a coarser slot's stamp; Typo fixes
Add a log statement
Merge pull request #209 from lakshmi-kannan/bf_fix_slot_stamp_npe

Fix NPE when updating a coarser slot's state