review: complete vignette - and add more details, background

[sckott]

However, the text of the vignette is clearly still unfinished. Given that the intended use of the package is pretty straightforward, the vignette doesn't need to be very detailed, but it would be helpful if it included a short paragraph at the beginning introducing the package, for example, as well as a paragraph explaining the differences between using fraudster versus the ch_* family of functions (even just adding the information currently in the helpfile for the package would be useful).