Add a support for sf objects

[Nowosad]

The sf package is the R implementation of Simple Features and starts to be a new standard for working with spatial data in R. More information at https://github.com/edzer/sfr and http://robinlovelace.net/geocompr/spatial-class.html.

Moreover, the development version of ggplot2 package already supports plots with sf object using a geom_sf() function - http://ggplot2.tidyverse.org/reference/ggsf.html. I think it could be very useful to have a possibility to add a north arrow and scale bar to maps with sf objects.

@oswaldosantos do you plan to add a support for sf objects?

[oswaldosantos]

Good suggestion @Nowosad. I'll work on that for future versions.

[Nowosad]

That's great! Yesterday I've created a geom_sf() map and a scale bar was the only thing missing.

[aakarner]

I think this is a great idea.

[rafapereirabr]

I agree it's a great idea. I was about to open another issue requesting the same development :)

[oswaldosantos]

Done! Please let me know if it's working well.

[rafapereirabr]

It is working beautifully here. Thanks again and congrats for the library! Grande abraço !