fn month_add_one(
year: ri16<-9999, 9999>,
month: ri8<1, 12>,
delta: ri8<-1, 1>,
) -> Result<(ri16<-9999, 9999>, ri8<1, 12>), Error>Expand description
Adds or subtracts sign from the given year/month.
If month overflows in either direction, then the year returned is
adjusted as appropriate.