This demo contains code to generate edge icons for turfs and to automatically place them on the map. It generates an 8-directional edge icon for each icon state. You can specify a custom mask icon to determine how exactly one turf will blend into the next.
Here's an example. This is the map without edges:
And this is the same map with the edges generated by this demo:
All you have to do is generate the edge icon state and set the edge_layer var for each turf.