GCM munging pipeline - Finalize compression option in netCDF pipeline

[hcorson-dosch-usgs]

As of now, the function in the targets sub-pipeline that generates a netCDF of the munged GCM driver data has a T/F argument to add compression, but this only works on a machine that has NCO net CDF operators installed. We ran into some errors setting that up on Windows. For now, we're moving ahead with the option for compression set to FALSE and the code set up to give an error message that compression is not yet fully supported if the user provides the argument compression = TRUE, but we'll need to revisit this for the final data release.

Jordan's suggestion upon revisiting the code is to:

do two things: 1) break out the compression code into another function that does the compression and nothing else and does its own clean-up (e.g., on.exit() deletion of the temporary files if something fails or the function completes cleanly) and 2) add information on the system libraries needed and how to get them.

[hcorson-dosch-usgs]

See Dave Blodgett's notes on his recommended approach here