Better compression for Ultracode in BMP

Also corrects colour shifting bug
File size is still bigger than it needs to be for Ultracode, but now uses 4bpp

backend/bmp.h

@@ -67,9 +67,9 @@ extern "C" {
     } bitmap_info_header_t;
     
     typedef struct color_ref {
-        uint8_t red;
-        uint8_t green;
         uint8_t blue;
+        uint8_t green;
+        uint8_t red;
         uint8_t reserved;
     } color_ref_t;