Simplify DLL hook mechanism

This change deletes the GetProcAddress hook and exports symbols
corresponding to the hooked functions from each hook DLL instead;
we stop at redirecting LoadLibrary/GetModuleHandle calls to the
hook DLL. This simplified approach has less hidden magic going on
behind the scenes and is more readily composable (i.e. a hook DLL
can export redirect symbols for more than one dynamically-loaded
DLL).

mu3hook/dllmain.c

@@ -35,7 +35,7 @@ static DWORD CALLBACK mu3_pre_startup(void)
 
     /* Hook Win32 APIs */
 
-    gfx_hook_init(&mu3_hook_cfg.gfx);
+    gfx_hook_init(&mu3_hook_cfg.gfx, mu3_hook_mod);
     serial_hook_init();
 
     /* Initialize emulation hooks */