Expects a full file path to the ReservoirStages.csv file, then
reads in the file using read.csv. The main advantage of this function is
renaming the columns to nicer names and extracting the units into something
much easier to read.
This function is also built to support the rvn_res_extract
function, which uses
the object created here for extracting by reference to the columns named
here, for example sub24.
ff is the full file path of the ReservoirStages.csv file. If the file is
located in the current working directory, then simply the name of the file
is sufficient.
The timezone is provided by the tzone argument as "UTC" by default, and should be adjusted by
the user to the local time zone as needed, based on the model run.