Add experimental calendarDistance function to compute “human” date differences in optional units of years, months, weeks and days.
There is some chance this works.
Remove some bugs from the calendarDistance computation
implement adjustment of earliest date based on calendarDistance.
Does work for some interesting cases
e.g. aged 1 month and 0 days on 1900-12-31 is correctly labelled impossible :-)
but crashes for age 1 year on 1904-2-29 :-(