Adding Fortran

Hi, 

I created the Fortran folder in the repository.

There is an example of how to write a netCDF file using netCDF F90 libraries

I am not sure if the previous pull have been propertly sent. It was about adding some stuff in python folder

Lluís

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I improved the netCDF output Fortran code. Now it uses a namelist and output using a namelist

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Finally fixing issue with spacemean in nc_var_tools.py