Feature Request: Add function for Brown-Forsyth test

[mtnbikerjoshua]

Example code:

grp <- as.factor(c(rep("lower", floor(dim(stop)[1] / 2)), 
                   rep("upper", ceiling(dim(stop)[1] / 2))))
leveneTest(pull(stop[order(stop$Speed), "resid"]) ~ grp, center = median)