Convert the game data into editable assets

assets/ now holds every track as a 16-colour indexed PNG (its palette is
the track palette) plus a text file of lap gates and height map, and
every vehicle as a PNG sprite sheet plus a text file with its name and
handling (moved out of the code). The build embeds assets/ instead of
unpacking the ADFs, so the disks are no longer needed to build either.

skids extract converts original disks to assets and checks each file
reads back identically; benchmark results from the assets match the
disks exactly. Assets win over disk data with the same name, and
--data assets picks up edits without a rebuild. assets/README.md
describes how to edit everything.

assets/vehicles/cow.txt

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+# Skids vehicle settings. Lines starting with # are comments.
+# The sprite sheet is cow.png: 32 headings across, 25 tilts down.
+name COW
+# top speed on tarmac, world pixels per second
+top 170
+# acceleration and braking, world pixels per second squared
+accel 150
+brake 320
+# sideways grip (higher = less sliding)
+grip 7
+# steering rate, radians per second
+turn 4.6
+# weight in collisions
+mass 1.4
+# speed and grip multiplier off the road
+offroad 0.9

assets/vehicles/f1.txt

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+# Skids vehicle settings. Lines starting with # are comments.
+# The sprite sheet is f1.png: 32 headings across, 25 tilts down.
+name FORMULA 1
+# top speed on tarmac, world pixels per second
+top 240
+# acceleration and braking, world pixels per second squared
+accel 210
+brake 320
+# sideways grip (higher = less sliding)
+grip 6.5
+# steering rate, radians per second
+turn 3.7
+# weight in collisions
+mass 0.9
+# speed and grip multiplier off the road
+offroad 0.45

assets/vehicles/midget.txt

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+# Skids vehicle settings. Lines starting with # are comments.
+# The sprite sheet is midget.png: 32 headings across, 25 tilts down.
+name MIDGET
+# top speed on tarmac, world pixels per second
+top 205
+# acceleration and braking, world pixels per second squared
+accel 185
+brake 320
+# sideways grip (higher = less sliding)
+grip 4
+# steering rate, radians per second
+turn 4
+# weight in collisions
+mass 0.85
+# speed and grip multiplier off the road
+offroad 0.6

assets/vehicles/mini.txt

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+# Skids vehicle settings. Lines starting with # are comments.
+# The sprite sheet is mini.png: 32 headings across, 25 tilts down.
+name MINI
+# top speed on tarmac, world pixels per second
+top 190
+# acceleration and braking, world pixels per second squared
+accel 200
+brake 320
+# sideways grip (higher = less sliding)
+grip 5.8
+# steering rate, radians per second
+turn 4.4
+# weight in collisions
+mass 0.8
+# speed and grip multiplier off the road
+offroad 0.55

assets/vehicles/police.txt

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+# Skids vehicle settings. Lines starting with # are comments.
+# The sprite sheet is police.png: 32 headings across, 25 tilts down.
+name POLICE
+# top speed on tarmac, world pixels per second
+top 215
+# acceleration and braking, world pixels per second squared
+accel 180
+brake 320
+# sideways grip (higher = less sliding)
+grip 5
+# steering rate, radians per second
+turn 3.5
+# weight in collisions
+mass 1.2
+# speed and grip multiplier off the road
+offroad 0.55

assets/vehicles/porsche.txt

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+# Skids vehicle settings. Lines starting with # are comments.
+# The sprite sheet is porsche.png: 32 headings across, 25 tilts down.
+name PORSCHE
+# top speed on tarmac, world pixels per second
+top 225
+# acceleration and braking, world pixels per second squared
+accel 190
+brake 320
+# sideways grip (higher = less sliding)
+grip 5.2
+# steering rate, radians per second
+turn 3.6
+# weight in collisions
+mass 1
+# speed and grip multiplier off the road
+offroad 0.55

assets/vehicles/truck.txt

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+# Skids vehicle settings. Lines starting with # are comments.
+# The sprite sheet is truck.png: 32 headings across, 25 tilts down.
+name TRUCK
+# top speed on tarmac, world pixels per second
+top 195
+# acceleration and braking, world pixels per second squared
+accel 140
+brake 320
+# sideways grip (higher = less sliding)
+grip 4.2
+# steering rate, radians per second
+turn 3
+# weight in collisions
+mass 1.8
+# speed and grip multiplier off the road
+offroad 0.75

assets/vehicles/vw.txt

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+# Skids vehicle settings. Lines starting with # are comments.
+# The sprite sheet is vw.png: 32 headings across, 25 tilts down.
+name BEETLE
+# top speed on tarmac, world pixels per second
+top 185
+# acceleration and braking, world pixels per second squared
+accel 160
+brake 320
+# sideways grip (higher = less sliding)
+grip 4.6
+# steering rate, radians per second
+turn 3.6
+# weight in collisions
+mass 1
+# speed and grip multiplier off the road
+offroad 0.55