Script to update timezone database from Olson data

This commit adds a new directory, db, which contains a Perl script, tz-erl, that generates a file that contains updated timezone data, in the format needed for the `tz_database.hrl` file, generated from the Olson timezone data.

Typing `make` will generate a `tzout` file that currently must be merged into the `tz_database.hrl` file manually.