fix: added missing ctor declarations

src/detail/fxn.hpp

@@ -16,6 +16,9 @@ namespace fxn
         struct Impl;
         Impl* m_Impl;
 
+        FxnManager();
+        ~FxnManager();
+
     public:
         static FxnManager& GetInstance();
         static void Destroy();

src/impl/dllmain.cpp

@@ -5,7 +5,7 @@ DWORD WINAPI ThreadProc(LPVOID lpParameter)
 {
     auto& fxnManager = fxn::FxnManager::GetInstance();
 
-    fxnManager.Initialize();
+    return TRUE;
 }
 
 BOOL APIENTRY DllMain(HMODULE hModule, DWORD ulReason, LPVOID lpReserved)