support different calendars

[Jamalianpour]

hello,
how can I use persian calendar and date on this plugin?

[JonasWanke]

Thanks for filing this issue! Currently, timetable only supports the gregorian calendar. As it's based on time_machine (which also supports three variants of the persian calendar), adding support for other calendar systems should be relatively easy.

I can try implementing it starting next week, though I don't know how long I'll need for it.

[Jamalianpour]

thank you.
I will wait for it.

[JonasWanke]

Because time_machine is not maintained very actively and still hasn't published a null-safe version to pub.dev, I dropped the dependency on it as part of the big refactor/rewrite (issue: #17, PR: #69). Instead, Timetable now uses Dart's built-in DateTime. Unfortunately, this also means that supporting other calendars is now out of scope as Dart doesn't support them either.