Merge pull request #3004 from henryzhao81/develop

To support customized cluster selection
Issue #2991
improved serialization interation with the document.
Merge branch 'develop' of github.com:orientechnologies/orientdb into develop
refactor new internal docs method naming.
added context variable  in sql queries #2871
added context variable $user in sql queries #2871
Merge branch 'develop' of https://github.com/orientechnologies/orientdb into develop
add logging information in the pool with available an used resurces. issue #2891
Merge branch 'develop' of github.com:orientechnologies/orientdb into develop
fixed database drop from console after server restart, issue #2918
fixed wrong pool close, that not properly clean the connections.
fixed json serialization problem #2845
fixed next() with size = 0
optimization of index usage on ORDER BY
Merge branch 'develop' of https://github.com/orientechnologies/orientdb into develop