format.beacon: Always encode shortcode as ASCII.
Add util.externalsort.GNUExternalSort
tracker.export: Always use ASCII for deriving dirs from shortcode
tracker.export: Rewrite w/ GNU Sort to avoid repeat full table scans.

Rewrite to avoid repeated full table scans by dump all the results into
a text files using SQLite's recommended scrolling window method. Then
calls GNU sort on the files and use results to finish writing the final
files.

Closes ArchiveTeam/terroroftinytown#17