goodness: perform a goodness of fit Monte-Carlo simulation

Perform a Monte Carlo calculation of the goodness-of-fit.

Syntax:           goodness [ <# of realizations>] [sim | nosim]

This command simulates  <# of realizations> spectra based on the model and writes out the percentage of these simulations with the fit statistic less than that for the data. If the observed spectrum was produced by the model then this number should be around 50%. This command only works if the sole source of variance in the data is counting statistics.The sim/nosim switch determines whether each simulation will use parameter values drawn from a Gaussian distribution centered on the best fit with sigma from the covariance matrix. The sim switch turns on this option, nosim turns it off in which case all simulations are drawn from the best-fit model.