Switches task keys to ISO YYYY-MM-DD. They sort, so finding every day
before today is a string compare instead of re-parsing each key.
Two things worth knowing. fromKey builds from date parts rather than
parsing a bare ISO string, which gets read as UTC and lands on the wrong
day west of Greenwich. addDays goes through setDate, so it stays on the
same calendar day across a DST change instead of adding a flat 24 hours.
Aculix Technologies