[Request] Support more calendar systems

Hi,

I would be glad if khal would not only support the Gregorian calendar, but other calendar systems too. For me the Hebrew calendar[1] would be interesting as it also defines some official civil Israeli dates (e.g. Jom haAtzma'ut).

But there are other calendar systems too that may be of interest for many other people (e.g. the Chinese calendar[2]). Wikipedia has an overview of calendar systems[3].

Regards, abelbabel

[1] https://en.wikipedia.org/wiki/Hebrew_calendar [2] https://en.wikipedia.org/wiki/Chinese_calendar [3] https://en.wikipedia.org/wiki/Calendar#Calendars_in_use