/// <summary>
/// Subscribes the specified topic.
/// </summary>
/// <param name="topicAsString">The topic.</param>
/// <param name="callback">The event.</param>
/// <exception cref="InvalidTopicException">Topic is invalid.</exception>
public void Subscribe(string topicAsString, Action <string, T> callback)
{
_subscribers.Add(SubscriptionTopic.From(topicAsString), callback);
}
public void Add(SubscriptionTopic topic, Action <string, T> callback)
{
_subscribers.Add(topic, callback);
}