See link direction

Hi,

Not really an issue rather an enhancement (or probably I'm hopeless and it's already practicable ^^). Is it possible to show the direction of a link with an arrow or a moving particle like vasturiano's 3d-force-graph :
- https://vasturiano.github.io/3d-force-graph/example/directional-links-arrows/
- https://vasturiano.github.io/3d-force-graph/example/directional-links-particles/ (nice but I think it's a perf killer with many many nodes)

Thanks for your work in any case! :)

No source files or tests are identified in the issue. Start by checking how ngraph.graph represents link direction, then compare the linked directional-arrows and directional-particles examples; done would mean a supported way to display link direction without unacceptable performance on large graphs.

Written by the indexing model from the issue text.