Document tzinfo

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+# `luatz.tzinfo`
+
+Provides a metatable for the timezone class.
+
+Created in `luatz.tzfile` and managed by `luatz.tzcache`;
+a timezone object contains information about a timezone.
+These objects are based on the information available in a "zoneinfo" file.
+
+Timezone objects should be considered opaque and immutable;
+so the following details can be skipped over.
+
+------------------------------------------------------------------------------
+
+The table contains a sequence of tables that describe the timezone at a given point
+using a `transition_time`: the unix timestamp (in UTC) that this definition starts, and
+a `info` table, which contains information about the change at that point:
+
+  - `gmtoff` (number) The offset from GMT (UTC) in seconds
+  - `isdst` (boolean): If this change was declared as daylight savings
+  - `abbrind` (number, abbreviation id)
+  - `abbr` (string): short name for this gmt offset
+  - `isstd` (boolean)
+  - `isgmt` (boolean)
+
+## `:find_current ( utc_ts )`
+
+Returns the relevant `info` table at the given utc timestamp for the given UTC timestamp.
+
+
+## `:localize ( utc_ts )`
+
+Convert the given UTC timestamp to the timezone.
+Returns the number of seconds since unix epoch in the given timezone.
+
+
+## `:utctime ( local_ts )`
+
+Convert the given local timestamp (seconds since unix epoch in the time zone) to a UTC timestamp.
+This may result in ambigous results, in which case multiple values are returned.
+
+e.g. consider that when daylight savings rewinds your local clock from 3am to 2am there will be two 2:30ams.