Determine the Soldiers At War palette

This commit also takes the first step towards making it configurable;
override `internal/palettes.DefaultPaletteName` at build time to choose
one palette over another. It would be nice to set this at runtime!

scripts/palette-from-pcx

@@ -0,0 +1,45 @@
+#!/usr/bin/env ruby
+
+if ARGV.size != 2
+    puts "Usage: $0 <filename.pcx> <Palette name>"
+    exit 1
+end
+
+FILENAME = ARGV[0]
+PALETTENAME = ARGV[1]
+
+f = File.open(FILENAME)
+
+# In a 256-colour PCX file, the palette is stored in the final 768 bytes as RGB
+# triplets, and the byte before that should be 0x0C: https://en.wikipedia.org/wiki/PCX#Color_palette
+f.seek(-769, IO::SEEK_END)
+
+raise "Check byte is wrong" unless f.read(1) == "\x0C"
+
+puts <<EOF
+package palettes
+
+import "image/color"
+
+var (
+	#{PALETTENAME}Palette = color.Palette{
+		Transparent,
+
+EOF
+
+# bytes.shift(3) # Ignore idx 0 so we can make it transparent
+
+256.times do
+  r, g, b = f.read(3).bytes
+
+  puts "\t\tcolor.RGBA{R: #{r}, G: #{g}, B: #{b}, A: 255},"
+end
+
+puts <<EOF
+	}
+)
+
+func init() {
+	Palettes["#{PALETTENAME}"] = #{PALETTENAME}Palette
+}
+EOF