[feature request] box arrowhead

[pmoura]

It would be possible to add a box (a square) arrowhead as provided by Graphviz (https://graphviz.org/docs/attr-types/arrowType/)? Similar to d2 circle and thus able to be styled with style.filled.

[jacobfriedman]

bump, following Logtalk, need this one

[adamratson]

Hey, I'd like to work on this as a first issue - I've got an MR ready that I'll post shortly!

[pmoura]

Thanks @adamratson and @alixander for implementing this feature!