new example: reachable hexes

[szikoramarci]

It is adding an example that showcases a new way of traversing hexes.

Starting from a coordinate, we'll get all reachable hexes we can reach in a certain step distance, avoiding obstacle hexes.

Why is it NOT the lightOfSight feature? Because we can reach a hex behind obstacles. We can reach if we have enough step points and the path from the start to the goal hex contains less or equal steps.

You can use this feature for example in games when you need to know how far a player can move ahead if there are traps, walls and, other creatures.

[szikoramarci]

Maybe the commits are messy. I hope it is not a problem. I can resolve that and get a cleaner commit history of that, but I guess before merging the GitHug can squash it automatically and use that description and title as the commit message and description, right?

Let me know if you see something I need to change, though.