added exponential distrbution + tests

new shortest-path walker (still todo)
modified dijkstra-path (new helper methods)

nav/dijkstra/DijkstraPath.h

@@ -43,8 +43,10 @@ public:
 	}
 
 	/** allow iteration */
-	decltype(path.begin()) begin()	{return path.begin();}
-	decltype(path.end()) end()		{return path.end();}
+	decltype(path.begin()) begin()								{return path.begin();}
+	decltype(path.end()) end()									{return path.end();}
+	const DijkstraNode<T>& operator [] (const int idx) const	{return *(path[idx]);}
+	size_t size() const											{return path.size();}
 
 
 	/** NANOFLANN: number of elements in the path */