/// <summary>
/// Connects nodes that ALREADY EXIST IN GRAPH
/// </summary>
/// <param name="fromNode"></param>
/// <param name="toNode"></param>
/// <param name="cost"></param>
public void ConnectDirected(GraphNode <T> fromNode, GraphNode <T> toNode, float cost)
{
Assert.IsTrue(ContainsNode(fromNode));
Assert.IsTrue(ContainsNode(toNode));
fromNode.AddNeighbour(toNode, cost);
}