merge latest change from upstream project (migrate to Olson TZs)

I've been using your excellent qdate for calculating timezone-specific time deltas, and I really like it. However, I have noticed that it fails to recognize some valid timezones and also fails to recognize timezones with Olson-standard underscores in place of spaces (e.g, "America/New_York"). I realized that this was because erlang_localtime originally was based on the C++ boost::local_time library rather than the proper Olson database, so it was missing a lot of data. Dmitry fixed that recently by accepting this pull request: dmitryme/erlang_localtime#10

I've integrated these changes into your changes to make this pull request so that qdate can work with more standard timezone data.

There is a unit test that fails due to dmitryme/erlang_localtime#12, a problem with the database causing DST to not be applied in a given date range for the "EST" timezone. It breaks [this unit test](https://github.com/choptastic/qdate/blob/13bab9fc8e3d9fe2f37f332b2b6c22d5989ebd0b/src/qdate.erl#L656) in qdate, so that problem may need to be resolved before this update can be made.