Allow steps to be non-diagonal

[gpascualg]

As per #2, allow to disable diagonal movement.

It is implemented by postprocessing the nodes and subdividing each diagonal step into two subsequent movements.

Note: I can not test it right now, it might take me some hours until I can

[gpascualg]

I just realized (through testing, better later than never) that it didn't work at all. I've fixed it in a further commit