Finish and polish new_game.c

Only one function is left undocumented. I tried to go into the assembly
to at least name it, but it clears fields in the save block that aren't
even documented yet.

include/item_menu.h

@@ -79,5 +79,7 @@ bool8 UseRegisteredKeyItemOnField(void);
 void CB2_GoToSellMenu(void);
 void GoToBagMenu(u8 bagMenuType, u8 pocketId, void ( *postExitMenuMainCallback2)());
 void DoWallyTutorialBagMenu(void);
+void ResetBagScrollPositions(void);
+
 
 #endif //GUARD_item_menu_H