yint: get interval as fraction of full years
In DDM: Death Registration Coverage Estimation

Either assume 365 days in the year, or get the precise duration.

1 2	yint(Day1, Month1, Year1, Day2, Month2, Year2, reproduce.matlab = FALSE, detect.mid.year = TRUE, detect.start.end = TRUE)

`Day1`	Day of first date
`Month1`	Month of first date
`Year1`	Year of first date
`Day2`	Day of second date
`Month2`	Month of second date
`Year2`	Year of second date
`reproduce.matlab`	logical. default `FALSE`. Assume 365 days in all years?
`detect.mid.year`	logical. default `TRUE`. Should June 30 and July 1 be considered .5?
`detect.start.end`	logical. default `TRUE`. Should Jan 1 always be 0 and Dec 31 always be 1?