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
Add SET CONSTRAINTS statement.
DEFERRABLE / INITIALLY DEFERRED.
merge MMcM: Parser support for SET CONSTRAINTS & DEFERRABLE

Merge pull request #101 from MMcM/sql-parser/set-constraints
https://github.com/FoundationDB/sql-parser/pull/101