examples: Add new assets and script for reveal demo

examples/demo/reveal/assets/convert.sh

@@ -8,10 +8,20 @@ done
 
 mv *.pal *.img ../nitrofiles/spr
 
+# The two backgrounds that share the palette have been edited to use 128 colors
+# each, so that the final combined palette is 256 colors in size.
+
+grit img8b_1.png img8b_2.png -ftb -fh! -gTFF00FF -gb -gB8 -pS -Oimg8b_1.pal
+
 grit nfl.png -ftb -fh! -gTFF00FF -gt -gB8 -mR8 -mLs
 
 for file in *.bin; do
     mv -- "$file" "${file%.bin}"
 done
 
+# This is required or the library will say that the second background doesn't
+# have a palette.
+
+cp img8b_1.pal img8b_2.pal
+
 mv *.pal *.img *.map ../nitrofiles/bg