* Handle maxspeed tags before surface and smoothness tags
Let's say we have a tertiary road with the following tags:
highway=tertiary
maxspeed=60
surface=gravel
smoothness=intermediate
While the maxspeed tag tells us the legal speed limit, the surface and
smoothness tags have much more effect on the real-world speed of a car.
We should process the maxspeed tags first, and then update the road's
forwards/backwards speeds according to any surface and smoothness tags.
For our hypothetical road the process in the car.lua profile now goes
like this:
1. Get default speed from profile (tertiary = 40 on line 150 of car.lua)
2. Change speed to 60 using maxspeed tag (WayHandlers.maxspeed function
in way_handlers.lua, lines 434-447)
3. Change speed to 40 using surface tag (WayHandlers.surface function
in way_handlers.lua, lines 360-363)
4. Check speed according to smoothness tag --- but because it's higher
than the speed according to the surface tag, leave the speed
unchanged (WayHandlers.surface function again, lines 368-371)
<ec36319232/profiles/car.lua (L150)>
<ec36319232/profiles/lib/way_handlers.lua (L354-L372)>
Note in step 3 above the speed's only changed from 60kph to 40kph
because it's a lower value. If the surface speed was higher than than
the previous value, the speed would remain unchanged. Another example:
highway=tertiary
maxspeed=60
surface=compacted
smoothness=intermediate
Here, although the profile's speed for compacted is 80, it would stay at
the lower value of 60 (see way_handlers.lua, lines 360-363).
<ec36319232/profiles/lib/way_handlers.lua (L360-L363)>