Move ZNC headers into own directory.

Yes, this breaks backwards compatibility, so what?
It's already broken with network stuff anyway.

modules/crypt.cpp

@@ -22,9 +22,9 @@
 //       It is strongly suggested that you enable SSL between znc and your client otherwise the encryption stops at znc and gets sent to your client in plain text.
 //
 
-#include "Chan.h"
-#include "User.h"
-#include "IRCNetwork.h"
+#include <znc/Chan.h>
+#include <znc/User.h>
+#include <znc/IRCNetwork.h>
 
 #define REQUIRESSL	1