CRAN Release v1.30.21

CHANGES IN VERSION 1.30.21

NEW FEATURES

o Enable the use of the Bioc-devel branch on R-devel during the 'summer'
  release cycle (@mtmorgan, #166)
o Allow `BIOCMANAGER_SITE_REPOSITORY` environment variable and
  `BiocManager.site_repository` option as a more permanent option for
  `site_repository` users (@LiNk-NY).
o Support for "time machine" CRAN installations has moved to BiocArchive
  and has been removed from the package (#151, @LiNk-NY)

MINOR CHANGES

o Correct links on help pages. See
  <https://github.com/Bioconductor/BiocManager/pull/160>; thanks
  @aitap
o Additional documentation provided for offline use of BiocManager in
  `?install` and in the main vignette (#165, @mtmorgan).