Added square style node joining to the plotting function

This is just an idea, don't feel obligated to accept...

I thought it was so fun to make merge requests that I've got another for you :). This one I am expecting to be a little more difficult to accept without further work . You might not like the 'for-loop' and I suppose you could do the definition of the edges in sets of three one step previous in the part where you first define edges in and out. I did it after that because of the differences between in and out that you already dealt with so I didn't have to, and then I would have several put several if statements inside your two if statements which I thought was more difficult to follow. I guess I need to update the package documentation as well. You'll have to give be some guidance with that if you want this feature in your package.