Now that the vignettes are pre-made and included as pdf files wrapped by tiny Rnw wrappers, we no longer need knitr, rmarkdown and pinp in the Suggests. (They are still used 'off-site' to produce the pdf files included in the tarball.) This makes the dependency graph a little simpler.

Checklist

• Code compiles correctly
• R CMD check still passes all tests
• Document the changes by file inChangeLog