Fix for broken URLs in CF Conventions document

[russ]

In the CF 1.4 document some URLs referencing the UCAR Unidata site result in "404 Not Found" errors or use deprecated paths for which permanent replacements are now available. Following is a list of external URLs that should be replaced, each followed immediately by its recommended replacement. References to the NetCDF Fortran Users Guide have been replaced by references to the corresponding text in the language-neutral NetCDF Users Guide. Unidata commits to supporting the replacement URLs through future web site and documentation reorganizations, so they will continue to be valid.

http://www.unidata.ucar.edu/packages/netcdf/guidef/guidef-15.html#HEADING15-0
http://www.unidata.ucar.edu/netcdf/docs/netcdf.html#NetCDF-Utilities

http://www.unidata.ucar.edu/packages/netcdf/guidef/guidef-7.html#HEADING7-67
http://www.unidata.ucar.edu/netcdf/docs/netcdf.html#Variables

http://www.unidata.ucar.edu/packages/netcdf/conventions.html
http://www.unidata.ucar.edu/netcdf/conventions.html

http://www.unidata.ucar.edu/packages/netcdf/guidef/guidef-13.html#HEADING13-12
http://www.unidata.ucar.edu/netcdf/docs/netcdf.html#Attribute-Conventions

http://www.unidata.ucar.edu/packages/netcdf/guidef/guidef-12.html#HEADING12-1381
http://www.unidata.ucar.edu/netcdf/docs/netcdf.html#NetCDF-Classic-Format

http://www.unidata.ucar.edu/packages/netcdf/guidef/
http://www.unidata.ucar.edu/netcdf/docs/netcdf.html

http://www.unidata.ucar.edu/packages/netcdf/index.html
http://www.unidata.ucar.edu/netcdf/index.html