Last release before migrating to 'PROJ6' and 'terra' package

This is the last release of fasterRaster before:

• migration to using GRASS 8+ (prior versions may still work... unclear!);
• migration to the PROJ6 geodetic and coordinate reference system (PROJ4 support may still work... unclear!);
• adoption of SpatRasters from the terra package for raster support (and dropping most support for Rasters from the `raster package);
• adoption of sf objects from the sf and SpatVector objects to represent vector (i.e., "shapefile) data (and dropping most support for Spatial objects from the sp package).

v0.6.0

Releasing into the wild!