[CALCITE-493] Add EXTEND clause, for defining columns and their types at query/DML time
[CALCITE-478] Move CSV tutorial (Siva Narayanan)

Close apache/incubator-calcite#21

Also, the following pull-requests were merged long ago:

Close apache/incubator-calcite#4
Close apache/incubator-calcite#19
Close apache/incubator-calcite#22
[CALCITE-282] Add {fn QUARTER(date)} function (Benoy Antony)

Close apache/incubator-calcite#13
Fix QUARTER function for null values and JDBC escape syntax
Make JsonHandler and JsonService thread-safe
[CALCITE-502] Support for grouping sets in AggregateUnionTransposeRule (Jesus Camacho Rodriguez)
[CALCITE-510] Support for grouping sets in AggregateExpandDistinctAggregatesRule (Jesus Camacho Rodriguez)

Close apache/incubator-calcite#27