Feature request: netgrossplot

[jslingsby]

Greetings

Thanks for a great package.

It would be great if you could add the option to facet by a variable in the netgrossplot. For example if you wanted to compare land cover change across areas with different land use types. I've played with retrofitting this with cowplot, but can't get rid of the extra legends and axis labels. Please let me know if you know of any other ggplot add-on packages that would allow it?

I haven't looked at your code to see how to implement this as I don't have time rght now, but if I get te chance I'll send a pull request.

Thanks!
Jasper