Handle maxspeed before surface and smoothness

Let's say we have a tertiary road with the following tags:

- maxspeed=60
- surface=gravel
- smoothness=horrible

The maxspeed tag tells us the legal speed limit, but the surface and
smoothness tags have much more effect on the real-world speed of a car.
In the default car profile, the gravel surface sets a driving speed of
40kph, and the horrible smoothness sets a driving speed of 10kph. It
seems to me that the tags should be processed in this order:

1. maxspeed
2. surface
3. smoothness

That is, maxspeed can be overridden by the surface tag, which can in
turn be overridden by the smoothness tag. In the case of our secondary
road, it would start with a driving speed of 60kph (from maxspeed),
which would be reduced to 40kph (from surface), and end at 10kph (from
smoothness).

However, before this change, the maxspeed tag is processed *after*
surface and smoothness: our road starts with a driving speed of 40kph
(from surface), it's reduced to 10kph (from smoothness), and then
*increased* to 60kph (from maxspeed).

This change alters the processing order so that maxspeed is processed
first, giving it the lowest priority of these three tags.

profiles/car.lua

@@ -431,9 +431,9 @@ function process_way(profile, way, result, relations)
     WayHandlers.hov,
 
     -- compute speed taking into account way type, maxspeed tags, etc.
+    WayHandlers.maxspeed,
     WayHandlers.speed,
     WayHandlers.surface,
-    WayHandlers.maxspeed,
     WayHandlers.penalties,
 
     -- compute class labels