Support much more DDL in NodeToString.

Including fixes to existing (createTable, dropTable, dropView) and new
(createSchema, alterTable, renameColumn, dropSequence and dropIndex).

Fixes #155
Fix unparsing GROUP_CONCAT
Added some tests for insert with values
The first item in a row consturctor can be SELECT
merge ScottDugas: Handle INSERT INTO t VALUES ((SELECT...), 3)

Merge pull request #158 from ScottDugas/sql-parser/handle-subquery-in-values
https://github.com/FoundationDB/sql-parser/pull/158
merge nathanlws: Handle more node types in NodeToString

Merge pull request #157 from nathanlws/sql-parser/more-nodetostring-fixes
https://github.com/FoundationDB/sql-parser/pull/157
Parse NULLIF as a plain routine invocation instead of transforming to IF.

Minor refactoring to reduce duplication of creating routine call nodes
and looking forward to removing JavaToSQL/SQLToJava nodes.
merge nathanlws: Parse NULLIF as a plain routine invocation

Merge pull request #159 from nathanlws/sql-parser/nullif-as-routine
https://github.com/FoundationDB/sql-parser/pull/159
Add a couple new isolation levels for what FDB can practically do.
merge MMcM: Add a couple new isolation levels for what FDB can practically do.

Merge pull request #160 from MMcM/sql-parser/isolation-levels
https://github.com/FoundationDB/sql-parser/pull/160