get_travel_distance: explain multi-stop-pass handling

	my $geo                   = GIS::Distance->new();

	my $distance_beeline

	  = $geo->distance_metal( @{$from_latlon}, @{$to_latlon} );

	# A trip may pass the same stop multiple times.

	# Thus, two criteria must be met to select the start/end of the actual route:

	# * stop name or ID matches, and

	# * one of:

	#   - arrival/departure time at the stop matches, or

	#   - the stop does not have arrival/departure time

	# In the latter case, we still face the risk of selecting the wrong

	# start/end stop. However, we have no way of finding the right one. As the

	# majority of trips do not pass the same stop multiple times, it's better

	# to risk having a few inaccurate distances than not calculating the

	# distance for any journey that lacks sched_dep/rt_dep or

	# schep_from/rt_from.

	my @route = after_incl {

		(         ( $_->[1] and $_->[1] == $from_eva or $_->[0] eq $from )

			  and ( defined $_->[2]{sched_dep} or defined $_->[2]{rt_dep} )

			  and ( $_->[2]{sched_dep} // $_->[2]{rt_dep} )->epoch == $from_ts )

		(

			( $_->[1] and $_->[1] == $from_eva or $_->[0] eq $from )

			  and ( not( defined $_->[2]{sched_dep} or defined $_->[2]{rt_dep} )

				or ( $_->[2]{sched_dep} // $_->[2]{rt_dep} )->epoch

				== $from_ts )

		)

	}

	@{$route_ref};

	@route = before_incl {

		(         ( $_->[1] and $_->[1] == $to_eva or $_->[0] eq $to )

			  and ( defined $_->[2]{sched_arr} or defined $_->[2]{rt_arr} )

			  and ( $_->[2]{sched_arr} // $_->[2]{rt_arr} )->epoch == $to_ts )

		(

			( $_->[1] and $_->[1] == $to_eva or $_->[0] eq $to )

			  and ( not( defined $_->[2]{sched_arr} or defined $_->[2]{rt_arr} )

				or ( $_->[2]{sched_arr} // $_->[2]{rt_arr} )->epoch == $to_ts )

		)

	}

	@route;