Shutting down compactionExecutor on db close
Merge pull request #2 from ajermakovics/master

Shutting down compactionExecutor on db close
checkpoint three changes

* fix: don't compare snapshots when comparing keys or ascendingIterator
  will behave unexpectedly

* feature: introduce key prefix compression to table block storage

* feature: introduce varint compression to entry storage
fix iterator bug: need to compare the key prefixes