Split out some unused asm and documented main.c (#242)

* Splitting out unused asm

* Documented main.c

include/PR/libultra.h

@@ -13,6 +13,6 @@ extern u32 osTvType;
 extern u32 osRomBase;
 extern u32 osResetType;
 extern u32 osMemSize;
-extern u8 osAppNmiBuffer[64];
+extern s32 osAppNmiBuffer[16];
 
 #endif /* _LIBULTRA_H */

include/common_structs.h

@@ -9,6 +9,8 @@ typedef s16 Vec3s[3];
 typedef u16 Vec3su[3];
 typedef s16 Vec4s[4];
 
+#define COURSE_NULL 0xFF
+
 typedef enum {
     /* 0x00 */ COURSE_MARIO_RACEWAY = 0,
     /* 0x01 */ COURSE_CHOCO_MOUNTAIN,