Global functions & macros are listed here.
 IMPLEMENT_XLLFN2 | Declare and describe an add-in function | 
 IMPLEMENT_XLLFN_EX | Declare and describe an add-in function | 
 XLL_FIX_STATE | Ensure that global data is in scope (MFC calls only) | 
 XllGetApp | Get a pointer to the global application object | 
 XllGetTypedApp | Get a correctly typed pointer to the global application object |