Note that this relies on a system call to awk. It probably won't work on Windows.
read_gsi_sim(path, sample_type, repunits = NULL)
path to the gsi_sim file
should be "reference" or "mixture" depending on what kind of file it is
the gsi_sim reporting units file. Has no effect if sample_type is "mixture". If sample_type is "reference" and this is left as NULL, then all collections will be put in the the "default_repu".