OPLA: minor changes
EHCluster and hash index source codes were merged.
Merge remote-tracking branch 'origin/master'
SQL: Fixed groupby with multiple fields and context variables
Merge branch 'master' of https://github.com/nuvolabase/orientdb
SQL: fixed last commit about GROUP BY and context variables against multiple fields
In memory implementation of hash table was removed.
Merge pull request #1394 from giastfader/master

Extends the SQL Method tojson() to accept format parameter
Fixed issue #1395
Merge branch 'master' of https://github.com/nuvolabase/orientdb
Fixed NPE in Tracker Lists
OPLA: improved performance with variable management (avoiding copy for most of the cases)
Revert "OPLA: improved performance with variable management (avoiding copy for most of the cases)"

This reverts commit 28548db57d472da31fc575ed1f63be034a2b031f.
OPLA: minor changes
LocalHashTable - all  issues related to metadata save procedure were fixed.
Merge remote-tracking branch 'origin/master'
SQL: fixed pick of multiple values in map. Example select tags['first', 'second'] from ...

Thread on:
https://groups.google.com/d/topic/orient-database/APf2w7AhOhA/discussion
Merge branch 'master' of https://github.com/nuvolabase/orientdb
Support gzip compression for response data
Support gzip compression for response data