Support for Date/Time Operations

Date/time operations are not sufficiently supported yet. Statements such as `"select (cast('2002-5-01' as date) + interval '60 days');"` cannot be parsed.

Such date/time operations are present in some TPC-DS queries, such as query 94.

[Postgres reference: Date/Time Functions and Operators](https://www.postgresql.org/docs/current/functions-datetime.html)