Transformation auxiliary data files

The mapping files to be used for the MAPPING option must be consistent
with the files generated by the SCRIP library to be used for the ` SCRIPR` transformations (see also section 4.3). The
files are NetCDF containing the following fields:

dimensions: src_grid_size = xxx ; dst_grid_size = xxx ; num_links = xxx ; num_wgts = xxx ; variables: int src_address(num_links) int dst_address(num_links) double remap_matrix(num_links, num_wgts)where

`src_grid_size`is a scalar integer indicating the total number of points in the source grid. This field is a netCDF dimension.`dst_grid_size`is a scalar integer indicating the total number of points in the target grid. This field is a netCDF dimension.`num_links`is a scalar integer indicating the total number of associated source and target grid point pairs in the file. This field is a netCDF dimension.`num_wgts`is a scalar integer indicating the number of weights per associated grid point pair (up to 5 are supported, see section 2.2.7). This field is a netCDF dimension.`src_address`is a one dimensional array of size`num_links`. It contains the integer source address associated with each weight. This field is a netCDF variable.`dst_address`is a one dimensional array of size`num_links`. It contains the integer destination address associated with each weight. This field is a netCDF variable.`remap_matrix`is a two dimensional array of size`(num_links, num_wgts)`. It contains the real weight value(s) associated with the source and destination address. This field is a netCDF variable.