Enable support for dates and percentages in Excel Database functions

[MarkBaker]

This is:

- [ ] a bugfix
- [X] a new feature

Checklist:

• Changes are covered by unit tests
• Code style is respected
• Commit message explains why the change is made (see https://github.com/erlang/otp/wiki/Writing-good-commit-messages)
• CHANGELOG.md contains a short summary of the change
• Documentation is updated as necessary

Why this change is needed?

The Excel Database functions don't just support basic numeric and string queries, but also allow formatted values like percentages (e.g. "<62%") and dates (e.g. ">=22-Feb-2021"). These structures are also permitted in functions like CountIf() and AverageIf().

This PR provides support for that functionality.

Still outstanding

• Support for Boolean expressions
• Support for wildcards in strings (e.g. ? and *)