Add new methods millisToExact and exactToMillis in munge.js.
Use these methods in munge.js, converter.js and segment.spec.js.
More consistently use underscores in all long numbers except for year numbers.
Because we now reduce Rats to their lowest terms, this allows me make some of the unit test assertions much "plainer". For example, something obtuse like new Rat(1_000_000_000n, 1_000_000_015n) can be replaced with a relatively comprehensible new Rat(86_400_000_000_000n, 86_400_000_000_000n + 1_296_000n).
millisToExactandexactToMillisinmunge.js.munge.js,converter.jsandsegment.spec.js.Rats to their lowest terms, this allows me make some of the unit test assertions much "plainer". For example, something obtuse likenew Rat(1_000_000_000n, 1_000_000_015n)can be replaced with a relatively comprehensiblenew Rat(86_400_000_000_000n, 86_400_000_000_000n + 1_296_000n).