reg_aucroc() function to calculate AUC for
regression models.sa_diff() output to separate staccuracies from
their differences. l- Use the (r+1)/(n+1) p-value
calculation from North et
al. (2003).sa_diff() function for bootstrapped-based
comparison of staccuracies.var_type() is no longer exported since it is really an
internal function.