Dijkstra Search algorithm

Hi all,

Added [Dijkstra search algorithm](http://en.wikipedia.org/wiki/Dijkstra%27s_algorithm). It is a generic implementation, to be used with any type of graphs (graphs, grids, etc...). It uses a map handler which provides an interface between the implementation and the custom graph. I have included three examples of handlers, for reference.
Tests have also been included.
And yes, anyone can rip it and use it straight, it's a full library per se! :+1: 

Regards,
Roland.