Transit isochrones

/isochrone now takes mode=transit with a depart_at: the area you can reach by walking and scheduled transit within each time band, on the same graph and agencies as transit routes.

• A transit band can be a MultiPolygon, because a ride drops you in areas you cannot walk between, and every one of them is kept
• A centre with no scheduled transit nearby is a 422 outside_coverage rather than a walking-only polygon
• Slower than road isochrones: about 1.8, 2.6 and 3.4 seconds for a single 30, 60 and 120 minute band from downtown Toronto