pass instance of std::ostream for logging from API

api/api.h

@@ -2,6 +2,7 @@
 #define API_H__
 
 #include <memory>
+#include <iostream>
 #include "Identity.h"
 #include "Destination.h"
 #include "Streaming.h"
@@ -12,7 +13,8 @@ namespace api
 {
 	// initialization start and stop	
 	void InitI2P (int argc, char* argv[], const char * appName);
-	void StartI2P ();
+	void StartI2P (std::ostream * logStream = nullptr);
+	// write system log to logStream, if not specified to <appName>.log in application's folder
 	void StopI2P ();
 
 	// destinations