Datetime handling

Leap years pose a challenge to datetime handling. If we index by day-of-year and align the years at Jan 1., then day 366 shows up at the end of the year for leap years. This makes visualization with month delineations difficult, as there would be this little offset in leap years.

Conversely, one could align the dates at the first of each month, this would create little gaps at the end of Feb. for non-leap years to align with the leap years on axes and labels.

Planning to dig into some of the manuals and published guidance to figure out how this is handled elsewhere and see if the USGS has a preferred method...