Add: Division/exactly()

[oscbyspro]

The following is super convenient when you need to ensure lossless behavior (#67).

extension Division where Quotient: BinaryInteger, Remainder: BinaryInteger {
    /// Returns the `quotient` and an `error` indicator.
    ///
    /// The `error` is set when the `remainder` is nonzero.
    ///
    @inlinable public consuming func exactly() -> Fallible<Quotient> {
        self.quotient.veto(!self.remainder.isZero)
    }
}