Add OrderByColumn assencding and nullsOrderedLow to toString output.

Fixes #81
Only keep values specified directly in CREATE SEQUENCE
merge nathanlws: Remove unspecified defaults from CreateSequenceNode

Merge pull request #96 from nathanlws/sql-parser/no-unspecified-sequence-defaults
https://github.com/FoundationDB/sql-parser/pull/96
merge nathanlws: Include all OrderByColumn members in toString

Merge pull request #94 from nathanlws/sql-parser/include-desc-order-by-tostring
https://github.com/FoundationDB/sql-parser/pull/94
Don't allow parameter markers in multi-statement parse, except locally within EXPLAIN and PREPARE.
merge MMcM: Don't allow parameter markers in multi-statement parse

Merge pull request #97 from MMcM/sql-parser/parameters-allowed
https://github.com/FoundationDB/sql-parser/pull/97
Add '$' as allowed character in identifiers.
Add a negative test too. Identifiers can't start with $
merge tjoneslo: Add $ as identifier

Merge pull request #99 from tjoneslo/sql-parser/add-$-as-identifier
https://github.com/FoundationDB/sql-parser/pull/99