Implement full support for "Business Day Conventions," including addition/subtraction of business days (supplementing the already-supported "business days between dates" functionality.) Business date conventions specify the business rule for adjusting dates so that they don't fall on holidays, such as "next business day," "preceding business day," "nearest business day, "next business day in same month--adjusting to previous business day if necessary," "previous business day in same month--adjusting to next business day if necessary"
Implement multiple timescales (e.g., UT0, UT1, UTC, TAI, apparent
solar...) Will at least implement UT1 and UTC--but the architecture will be extensible.
Complete all documentation.
Implement the Chinese Calendar.
Implement the Astronomical Hijri (Islamic) Calendar.