roundExtent rounds the coordinates of the extent of a Raster* to a number of digits specified.
This can be useful when dealing with a small inprecision in the data (e.g. 179.9999 in stead of 180).
nudgeCoords takes the floor (lower integer) of the mimumum x and y of the exent and the ceiling (upper integer)
of the maximum x and y of the extent. Thus returning a RasterLayer with an extent of rounded coordinates and that
always includes the original extent. This can be useful when creating raster objects based on the extent of other objects.