[R-pkgs] roxygen2

[Peter Danenberg]

Hadley Wickham refactored roxygen, making it more maintainable and
robust; the changes are so significant that we decided to nominate it
roxygen2:

  http://cran.r-project.org/web/packages/roxygen2/index.html

Some highlights:

  * it's faster;
  * usage has been improved (the @usage tag should be obsolete);
  * @rdname merges documentation for multiple functions into one file.

For details, see:

  https://github.com/klutometis/roxygen/blob/master/NEWS