Create a GUI that displays all vignettes for installed packages.
The user can choose to view the source file for building the vignette
or the final .pdf file.
showVignettes(package)character string specifying package name that exists in the user's R library
If the argument package is not specified, the function
will look for vignettes in all packages installed on the user's
system. The user can choose to view the source file
for building the vignette (usually *.Rnw or *.Snw files)
or the final build from the source code (*.pdf).
showVignettes uses the PBSmodelling function
openFile to display the .Rnw and .pdf files
using programs that the system associates with these extensions.
On systems that do not support file extension associations, the
function setPBSext can temporarily set a command to associate
with an extension.