Hello samspot, thank you for the helpful feedback!
I implemented the vi-key support like it is described here. Like suggested I implemented the [.]-key to skip a turn.
Could you please test for me if the implementation is correct since I am not used to these controls myself.
(For QWERTZ-keyboard-layout users [z] can also be used for moving up-left. Don't know if this makes any sense, but it's possible now.)