Support Range datatype

[KodrAus]

This is a new datatype introduced in 5.2 for value ranges. See here.

Looks like we could represent it as:

struct DateRange<F> {
    gte: Date<DefaultDateMapping<F>>,
    lte: Date<DateRangeMapping<F>>,
}

Some things to think about:

• Support for other bounds; gt or lt. Anything that can be represented by gt or lt can be done by gte and lte so not a big priority.

Ranges also support number types so they'll need to be added.

[KodrAus]

I think it's worth copying Rust's ranges, so the lower bound is gte and the upper bound is lt.

[KodrAus]

For completeness these bounds could also be represented as enums:

enum LowerBound<T> {
    LessThan(T),
    LessThanOrEqual(T),
}

enum UpperBound<T> {
    GreaterThan(T),
    GreaterThanOrEqual(T),
}

So you could choose whatever bounds you want, but won't have the invalid case of specifying both lt and lte.