Invalid arguments passed to nplot() now raise an error.
Figures with legends are not drawn twice.
Values supported by nplot() are now included in all methods (helps with
argument completion).
Changed some default values for better results.
The arguments skip.vertex, skip.edges, and skip.arrows now work as
documented.
New function nplot_legend() helps to add legends to the figure.
New nplot() method for matrices.
New feature: Gradients.
The argument sample.edges now work as expected.
vertex.color, vertex.size, and vertex.nsides now accepts formulas.
edge.width now accepts formulas.
New function: locate_vertex().