add comments, example

git-svn-id: https://svn.r-project.org/R/trunk@66009 00db46b3-68df-0310-9c12-caf00c1e9a41
Add Rd macros for package overview pages, get promptPackage() to use them.

git-svn-id: https://svn.r-project.org/R/trunk@66010 00db46b3-68df-0310-9c12-caf00c1e9a41
Fix bug in options(help.try.all.packages=TRUE), set it to TRUE when asking for package overview help.

git-svn-id: https://svn.r-project.org/R/trunk@66011 00db46b3-68df-0310-9c12-caf00c1e9a41
help defaults to the loaded packages, not just those on the search list.

git-svn-id: https://svn.r-project.org/R/trunk@66013 00db46b3-68df-0310-9c12-caf00c1e9a41
Better implementation of package?foo

git-svn-id: https://svn.r-project.org/R/trunk@66015 00db46b3-68df-0310-9c12-caf00c1e9a41