(#583) - compact callback after compaction's done

Now http adapter behaves like others. The code manually pings
database to check if it's done compaction.
(#583) - uncomment compaction test

This test was failing due to http compaction took some time
and callback was fired before it finished. Now it's fixed
(#583) - add compaction documentation
Merge pull request #593 from neojski/583-call-compact-callback-when-done

583 call compact callback when done