document footpath accessors

List of URLs, may be empty. Each URL poinst to an HTML map of the departure

station.

=item $part->footpath_duration

Walking duration when transferring before / after / during this trip

in minutes. The meaning depends on the value of B<footpath_type>.

=item $part->footpath_parts

Returns a list of [I<type>, I<level>] arrayrefs describing the

footpath. For instance, ["ESCALATOR", "UP"], ["LEVEL", "LEVEL"],

["STAIRS", "UP"] means first taking an escalator up, then walking a while,

and then taking a flight of stairs up again.

The content of I<type> and I<level> comes directly from the EFA backend. At

the moment, the following values are known:

=over

=item type: ESCALATOR, LEVEL, STAIRS

=item level: DOWN, LEVEL, UP

=back

=item $part->footpath_type

type of this footpath, passed through from the EFA backend. The value

"AFTER" indicates a footpath (transfer) after this route part. The value

"IDEST" indicates that this route part already is a footpath (aka a walking

connection between two stops), so the B<footpath> accessors contain redundant

information. Other values such as "BEFORE" may also be returned, but this is

unknown at this point.

=item $part->regular_notes

Remarks about the line serving this connaction part. Returns a list of