Add wilcoxon report

[hejtmy]

Add simple wilcox report for us, who need non parrametric tests as well :)

> smaller_iris <- iris[iris$Species %in% c("virginica", "setosa"),]
> wilcox.test(smaller_iris$Sepal.Length ~ smaller_iris$Species)

	Wilcoxon rank sum test with continuity correction

data:  smaller_iris$Sepal.Length by smaller_iris$Species
W = 38.5, p-value < 2.2e-16

to output Z = 38.5, p < .01

[hejtmy]

I might have a look into that myself when I have some time, your code is well written, shouldn't be an issue to add this function

[dgromer]

Will take a look into that when I have some spare time.