Fix anti meridian cases

[agrouaze]

address #172
after testing a solution that would go beyond the raise Error in case of antimeridian, it appears that rastering methods (map_raster and _load_rasters_vars) can simply not handle such geolocations (at least without heavy modification of the function).
Trying the rastering methods leads to artifacts:

So it is decided that the comments will be clearer in the code and in the Exception() msg.