Changes

• Add lau/tzdata package as dependency for loading Olson timezone information
• Refactor Timezone module to use Tzdata for loading the tz database
• Refactor TimezoneInfo struct to reflect that the information is for a single period, rather than all periods
• Remove Timezone.Dst module, as it is no longer needed
• Refactor timezone related APIs to take a DateTime or Erlang datetime tuple in most places where a timezone is being loaded, as it is necessary to know which point in time to fetch zone info for.
• Update tests.

This is a significant update! Please post issues as you encounter them and I will address ASAP. This release will likely be the last prior to a 1.0-RC.