Mention pkgdown config options like authors

[maelle]

http://pkgdown.r-lib.org/reference/build_home.html?q=authors#yaml-config-authors (so if one lists rOpenSci as fnd, one can add its logo!)

[maelle]

Also, function grouping in reference. If posssible by tags that make grouping exist in the docs as well (am exploring has_concept these days).

[maelle]

Grouping with has_concept is awesome.

The best thing to do seems to be using @family roxygen2 tags in function documentation, this way

• there are cross references in the local documentation.
• current dev roxygen2 transforms all these tags to concept tags as well, that can be used by has_concept in a pkgdown config file to easily obtain grouping in the reference page.

Example in the wild: https://github.com/lockedata/optiRum