The time::date module implements the common international Gregorian chronology,
based on the astronomically numbered proleptic Gregorian calendar and the ISO
week-numbering calendar, as per the ISO 8601 standard, and the common 24 hour
clock. It provides [[date]], a representation of civil date/time and a optimized
extension of the [[time::chrono::moment]] type. The [[time::chrono::]] module
has many useful functions which interoperate with dates. Any [[time::chrono::]]
function which accepts *moment also accepts *date.

Dates are created using [[new]], [[now]], [[localnow]], or a "from_" function.
Alternatively, the [[virtual]]/[[realize]] interface can handle uncertain or
invalid date/time information, and construct new dates incrementally and safely.
The observer functions ([[year]], [[hour]], etc.) evaluate a date's observed
chronological values, adjusted for its associated [[time::chrono::locality]].
Use [[in]] to localize a date to another locality; consult [[time::chrono::tz]].
See [[parse]] and [[format]] for working with date/time strings.

Date arithmetic operations are categorized into "timescalar" or "chronological".
Timescalar uses [[time::duration]]; see [[add]], [[time::chrono::diff]].
Chronological uses [[period]]; see [[reckon]], [[pdiff]], [[unitdiff]],
[[truncate]]. Note that calendrical arithmetic is highly irregular due to field
overflows and timezone discontinuities, so think carefully about what you want.
