In a topic file, a \link to a topic of the same package is a relative link. @seealso keeps its lists, and the footer no longer links to ../../pkgmd/.
The index README.md groups topics under the reference: sections of _pkgdown.yml, or by \concept when that file is absent. Topics in no group go under ## Other.
R6 method links go to lowercase anchors on the same page, and inherited methods are a list. Other \if{html}{\out{}} HTML is dropped. A list in \value{} stays a list.
New build_site() writes a front page, the reference and every .Rmd vignette as GitHub Markdown.
