* Enable support for dates and percentages in Excel Database functions, and CountIf/AverageIf/etc
* Enable support for booleans in Excel Database functions
* Refactor the Excel Database functions; and rewrite the query building to fix a bug with complex multi-criteria queries that involve both AND and OR conditions
* Fix handling for empty cells and NULL values in searches
* Expand unit tests; and add TODOs for dates, percentages, and wildcard text comparisons