Despite the fact that sp23design.Rnw is an Rnw file, it is not
really a vignette. It is the implementation of this package written in
a semi-literate style to ensure correctness of the (rather involved)
mathematics. This is really for my own sake since I don't want
to re-derive all those formulas again, but others might find it useful. 
Therefore, I have placed a pdf version of the processed output in
the doc directory.

Also, sp23design.Rnw file is processed using knitr.
