``track-list`` is now filtered by the currently selected edition
add ``edition-list/N/metadata`` sub-property
add ``program_id`` support to EDL ``!track_meta`` header
add ``--flatten-editions`` option to disable program-based edition grouping
add ``track-list/N/program-ids`` sub-property
deprecate ``track-list/N/program-id`` in favor of ``track-list/N/program-ids``