Save files with multiple regions

In the future, we might want to save netCDF files where the region dimension is longer than 1 (for example, spatial aggregation for multiple countries).

In this case, the metadata of the netCDF files needs to accurately describe each region.

Currently, the metadata looks like this:

	int region(region) ;
		region:name = "region" ;
		region:long_name = "NAO region" ;
		region:lats_range = "20, 80" ;
		region:lons_range = "-80, 40" ;

The region dimension itself could have multiple values, but it's unclear if its attributes (long_name, lats_range, lons_range) can. I have not seen any netCDF file where the attributes of a dimension can have more than one value. Therefore, the main issue would be coming up with a way to save the metadata that is correct and sufficiently descriptive.

@nperez, if you have any examples of files (in /esarchive or that we can download) that contain multiple regions, they would be very helpful. If there's any other requirement you can think of, please let me know.

Thanks,

Victòria