Implementation of A-star search algorithm to find the shortest path in 2D polygon maps.

The basic usage is;

# computes the heuristic cost between two nodes
def heur_fun(node_a, node_b) do
  ...
end

# Define a graph
graph = %{
  node_1 => [
  {node_2, cost_1_2}, {node_3, cost_1_3},
  ],
  node_2 => [
    {node_3, cost_2_3}, {node_4, cost_2_4},
  ],
  ...
}

# Do A-star search
state = Astar.search(graph, node_1, node_z, &heur_fun/2)

# Extract path
path = Astart.path(state)
[node1, ..., node_z]