Function astar 

pub fn astar<'a, F: Fn(Vec2, Vec2) -> f32>(
    tree: &BSPTree,
    portals: &Portals,
    start: Vec2,
    end: Vec2,
    heuristic: F,
    info: SearchInfo,
    path: &'a mut Option<Path>,
) -> Option<&'a mut Path>