Remove dependence on maptools, rgdal, and rgeos

[dicook]

I think that all the dependencies on map tools, rgeos, rgdal are removed now.

The example code is wrapped in \dontrun which CRAN frowns on these days. You'll need to make example code actually run.

I have converted the extra-data/sF_XXX objects to be sf objects.

Some of the current example code uses data from data-raw which is the old type of spatial polygon. When I converted these and ran the sample code, as much as I could work out, the changes were working ok.