Log Message:
Update all R packages to canonical form.

The canonical form [1] of an R package Makefile includes the
following:

- The first stanza includes R_PKGNAME, R_PKGVER, PKGREVISION (as
  needed), and CATEGORIES.

- HOMEPAGE is not present but defined in math/R/Makefile.extension to
  refer to the CRAN web page describing the package.  Other relevant
  web pages are often linked from there via the URL field.

This updates all current R packages to this form, which will make
regular updates _much_ easier, especially using pkgtools/R2pkg.

[1] http://mail-index.netbsd.org/tech-pkg/2019/08/02/msg021711.html