Loads the DLL (Dynamic Linked Library) called dllfilename into FMSLogo.
Once loaded you can call functions with DLLCALL.
When you have finished, you can unload the DLL with DLLFREE.
You may load more than one DLL at a time.
Loading a DLL that is already loaded simply increments a reference count and requires an additional call to DLLFREE to actually unload the DLL.