Chanukah candle-lighting times & performance improvements

This release changes the behavior of Chanukah candle-lighting times. In versions 2.3.0 and earlier, each day of Chanukah would be represented as 2 Events: one HolidayEvent such as Chanukah: 3 Candles and a separate CandleLightingEvent with the corresponding time. In version 2.4.0 and later, Chanukah events are now emitted as a single HolidayEvent with extra attributes eventTime and eventTimeStr.

In addition, this release improves performance of HDate to Date conversion by caching the absolute Julian Days, and a minor memory improvement to the Event class by removing the Event.getAttrs() function and assigning optional attributes directly to the underlying object.