public static string Create(string start, string end, string subject)
{
var innerPair = new KeyValuePair<string, string>(start, end);
var outerPair = new KeyValuePair<string, KeyValuePair<string, string>>(subject, innerPair);
return outerPair.SerializeToJsonObject(); // {"Key": subject, "Value": {"Key": start, "Value": end}}
}