Make_closea_masks.py is a python routine to create closea mask fields
based on the old NEMO closea index definitions.  Details of the grid
and the bathymetry are read in from the domain_cfg.nc file and the
closea_mask* fields are appended to the same domain_cfg.nc file.

To use this routine:

  1. Provide domain_cfg.nc file for your configuration.

  2. Define closed seas for your configuration in Section 2 
     using indices in the old NEMO style. (Read the comments on 
     indexing in Section 2!). Examples are given for eORCA025 
     (UK version) for the three different options:
        - just defining closed seas (and distribute fluxes over global ocean)
        - defining closed seas with a RNF mapping for the American Great Lakes to the St Laurence Seaway
        - defining closed seas with an EMPMR mapping for the American Great Lakes to the St Laurence Seaway

  3. Choose whether to mask the closea_mask* fields. This is not required
     but makes the fields easier to check.

  4. Module can be run in python or from linux command line if you
     change the top line to point to your python installation. If 
     using from command line, type "make_closea_masks.py --help"
     for usage.