- Reorganization of operators.
- Added ORDER_BY construct and core.Sort() node used by ORDER_BY.
- Added flags to each `Node` that can hold a small information (additional keywords, etc...).
- Added DISTINCT/ALL to aggregation functions (Flags).
- Added DISTINCT/ALL to UNION/INTERSECT like selects.
- Split Query class into `SelectQuery`, `InsertQuery, `UpdateQuery` and `DeleteQuery`.
- Minor bug fixes.
- Added mode tests.