Replace `maptools` and `rgdal`

[pdil]

• Replaced maptools::elide with sp::elide
• Replaced rgdal with sf as sp now depends on it
• This should also resolve CRAN warnings/errors related to missing functions (e.g. maptools::elide)

See https://r-spatial.org/r/2023/04/10/evolution3.html for more information

fixes #57 fixes #70 closes #68