v0.3.1

• Some roads with motor_vehicle=no were no longer in cyan due to a logical
  error, this is now fixed. See #222.
• Better rendering of cycleways on bridges, to avoid them being drawn below
  the associated highway.
• Make pedestrian streets smaller at high zoom.
• Steps are now rendered the same color as footway.
• Surface is shown from Z14, to have track surfaces at this zoom.
• Traffic lights are now rendered from Z18 instead of Z17.
• Buildings 3D effect is now rendered from Z18 instead of Z17.