[Feature] Node cost

[wlfio]

Whilst working on my own project i found i wanted to include a cost into node, so that the pathing would avoid them if possible.

So I have implemented it and will let you decide if you want it. (this also addresses issue #14)

I have implemented it so that it is non breaking, as it only enables if the developer sets a previously non existant option.

0 = walkable
2 = walkable but not prefered
5 = not walkable

let myMatrix = [
  [0, 0, 2, 2, 2, 2, 0, 0],
  [0, 0, 2, 2, 2, 2, 0, 5],
  [0, 0, 5, 5, 0, 5, 5, 0],
  [0, 0, 5, 0, 0, 0, 5, 0],
  [0, 0, 0, 0, 0, 0, 5, 0],
  [5, 5, 5, 0, 5, 0, 5, 0],
  [0, 0, 0, 0, 5, 0, 5, 0],
  [0, 0, 5, 0, 0, 0, 0, 0]
];

this.aStarInstance = new AStarFinder({
  grid: {
    matrix: myMatrix,
    maxCost: 5,
  }
});

Examples:

I wanted the wires to avoid blocking the pins on the chips if possible to make it easier for later wire to path to them.

So with my cost feature i added an extra cost to the nodes just above and below a chip. now it paths like this.

But if it MUST go into a space because going around is impossible or far too costly it will

Developers using the feature can set their own cost values to make things even les desirable if they wished, this could for instance be used in a game to avoid different types of terrain if possible, unless the path arround is far too long.