A Fortran namelist I/O module

This module is intended to provide a small upgrade to native Fortran namelist functionality.

All model parameters are loaded from nml files. Each model should have a default parameter file (eg, model.nml) that is loaded first, which ensures that all parameters are initialized with realistic values. Then, for a given domain, a parameter file can be specified (eg, Greenland.nml) that overwrites the default parameter values. In principle, the domain-specific parameter file should contain parameters from all relevant models. The key to this method is to properly specify the name of each group of parameters in the file.