Grids handling
It is time that MeteoIO start handling grids in a more convenient and powerful way. Each plugin should have a method that provides the list of available grids for a given time range:
std::vector< std::pair<Date, std::vectorMeteoGrids::Parameters > > listGrids(const Date& start, const Date& end)
Then the Gridsmanager could define which grids need to be retrieved in order to build the requested grid (for example, building an ISWR grid out of direct and diffuse grids). This would also allow us to temporally resample the gridded data at some point.
The Gridsmanager / Meteo2DInterpolator should also now implement all the downsampling / points retrieval strategies
Another improvement would be to be able to apply filters on grids. A new section [GridFilters] would contain the filter definitions (so the hard-coded processing in Meteo2DInterpolator would be obsolete).