Provide interface to tz/zoneinfo database

[AshleyYakeley]

Merge in functionality from these packages:

• timezone-series
• timezone-olson
• leapseconds
• timezone-unix

[AshleyYakeley]

Blocked on ygale/timezone-olson#3.

[AshleyYakeley]

These depend on bytestring, binary, and extensible-exceptions, which are not core libraries.

[AshleyYakeley]

Never mind, bytestring and binary are core libraries. extensible-exceptions is not, but it is probably removable.

[mulderr]

@AshleyYakeley Did you also have a look at tz? This PR is a draft of POSIX TZ support for tz. Hoping @klao will manage to make sense of my code and put together a final version. However, it also adds dependency on attoparsec. This is rather far fetched but do I understand correctly that if we were even hoping of thinking what I'm currently thinking then we would have to manage without attoparsec or in fact without anything that does not currently ship with GHC?