Tzfile support

[lifthrasiir]

So that we don't have to separately ship something like pytz rely on the fragile, sometimes incorrect and unreliable OS APIs :)

[lifthrasiir]

Note that I do have a (local) branch with a basic tzfile handling. POSIX tz rule string seems hard to deal with though (this is a part of tzfile v3 and required for describing the future transitions).

[ehsanul]

I'm interested in tackling this with some guidance @lifthrasiir, mainly since I need to have DST support in Chrono. Would that be ok?

And do you still have your branch with basic tzfile handling somewhere?

[lifthrasiir]

@ehsanul Yes, I still have a branch around; the main blocker was several edge cases around TzRule (which is a part of TzFile v3), and Chrono 0.3 (still in development, sorry :S) would have necessary changes to avoid such edge cases.

For now, though, you can make an individual type for time zones observing DST.

[pitdicker]

Tzif support including TzRule was added in #677.
I think it would be could if this could be extended to more timezones than just Local, but that is not what this issue is about.