Change memory layout of Image, so it's not drawn upside-down by SDL

src/image.rs

@@ -24,7 +24,7 @@ impl OutputImage {
 
     pub fn set_color(&mut self, row: u32, column: u32, red: u8, green: u8, blue: u8) {
         assert!(row < self.height && column < self.width);
-        let index = ((row * self.width + column) * self.channels) as usize;
+        let index = (((self.height - (row + 1)) * self.width + column) * self.channels) as usize;
         self.pixel_data[index] = red;
         self.pixel_data[index + 1] = green;
         self.pixel_data[index + 2] = blue;