doc references

[brry]

Throughout the homepage, redirected man pages like
https://www.rdocumentation.org/packages/rdwd/topics/fileIndex
should be replaced with
https://www.rdocumentation.org/packages/rdwd/topics/index

Something like
helplink <- function(doc, topic=doc) paste0("[",doc,"](https://www.rdocumentation.org/packages/rdwd/topics/",topic,")")
should do the trick, and then I just need to check manually which manpages have an alias.