copy-tags: Use FileTags::copy() method.

        public void copy() {

            var time = Util.get_file_time(source);

            if (source_tags.artist != null)

                target_tags.artist = source_tags.artist;

            if (source_tags.title != null)

                target_tags.title = source_tags.title;

            if (source_tags.album != null)

                target_tags.album = source_tags.album;

            target_tags.year = source_tags.year;

            if (source_tags.track != -1) {

                target_tags.track = source_tags.track;

                if (source_tags.total != -1)

                    target_tags.total = source_tags.total;

            }

            target_tags.disc = source_tags.disc;

            if (source_tags.genre != -1)

                target_tags.genre = source_tags.genre;

            if (source_tags.comment != null)

                target_tags.comment = source_tags.comment;

            if (source_tags.composer != null)

                target_tags.composer = source_tags.composer;

            if (source_tags.original != null)

                target_tags.original = source_tags.original;

            if (source_tags.cover_picture != null)

                target_tags.cover_picture = source_tags.cover_picture;

            if (source_tags.artist_picture != null)

                target_tags.artist_picture = source_tags.artist_picture;

            if (source_tags.band != null)

                target_tags.band = source_tags.band;

            target_tags.copy(source_tags);

            target_tags.update();

            target_tags = null;

            Util.set_file_time(source, time);

            Util.set_file_time(target, time);

        }

        private const string CONTEXT =

            "SOURCE TARGET - Copy Id3v2.4.0 tags";

            "SOURCE TARGET - Copy Id3v2.4.0 standard tags";

        private const string DESCRIPTION =

            "The SOURCE and TARGET MP3 files need to exist.\n";