mu3hook/unity.c: hook Unity plugin DLLs

- Unity loads plugin DLLs and Mono dynamically.

- Ongeki uses Criware for videos so hook the Criware plugin DLL so the
  path hooks load the videos from the hooked paths.

mu3hook/unity.h

@@ -0,0 +1,3 @@
+#pragma once
+
+void unity_hook_init(void);