Added ability to supply JSON from standard input

sdl_helpers.cpp

@@ -141,15 +141,20 @@ bool read_config_json(json& cfg, const string& filename, ostream* log)
 	{
 		if (nullptr != log)
 		{
-			*log << "Could not open config.json" << endl;
+			*log << "Could not open config file" << endl;
 		}
 		return false;
 	}
 
+	return read_config_json(cfg, cfg_file, log);
+}
+
+bool read_config_json(json& cfg, istream& in, ostream* log)
+{
 	// Parse with comments
 	try
 	{
-		cfg = json::parse(cfg_file, nullptr, true, true);
+		cfg = json::parse(in, nullptr, true, true);
 	}
 	catch (const std::exception &e)
 	{