Function a_star 

pub fn a_star<Edges, Heuristic>(
    edge_storage: &mut Edges,
    start: VHandle,
    goal: VHandle,
    vertices_count: usize,
    h_score: Heuristic,
) -> Option<Stack<VHandle>>
where
    Edges: EdgeStore,
    Heuristic: Fn(VHandle, Edge) -> Weight,

A* algorithm f_scores are sums of (distances + heuristic) from start to current vertex h_scores are heuristic values from start to current vertex g_scores sums of distances from start to current vertex. Not used purely in this implementation, but summed up to f_scores