Added a level script function to easily set a skybox for each area

In your level script add the function
CHANGE_AREA_SKYBOX(Area ID, Skybox Segment Start, Skybox Segment End) .

include/level_commands.h

@@ -190,6 +190,12 @@
     CMD_PTR(romEnd)
 #endif
 
+#define CHANGE_AREA_SKYBOX(area, segStart, segEnd) \
+    CMD_BBH(0x3D, 0x0C, area), \
+    CMD_PTR(segStart), \
+    CMD_PTR(segEnd) 
+    
+    
 #define INIT_LEVEL() \
     CMD_BBH(0x1B, 0x04, 0x0000)