edge width is not used #17

It seems that the edgewidth is not used in the function nplot. We need to ensure that the code is explicitly taking the edge.width parameter and setting the linewidth when creating the grob (graphical object from the grid package). We need to investigate the code to see if (a) the linewidth reflects the edge weight, and (b) if it is passed in the correct form. We need the following as well:

1. Try to replicate a bug and inspect visually and in the code whether the width is passed or not.
2. Fix the bug, update the NEWS.md file.
3. Add an example in the vignette "graph drawing with netplot" that shows how changing the edge weight works. Perhaps also using the set_edge_par function example as well. This should illustrate how the edge.width.range parameter works too.