Add post-processed NOMADs files

[jameshalgren]

We need to add another function to prepare file names for this location: https://nomads.ncep.noaa.gov/pub/data/nccf/com/nwm/post-processed/WMS/

The files at that URL are combined so that a single file contains a complete forecast -- i.e. there are 18 hours of output in the shortrange file, 240 hours in the medium range file, and so forth. There are some advantages with using these files if the user is downloading the file for repeated access.