CRAN Release v0.5.0

Packrat 0.5.0

• Packrat now supports both of BiocManager and BiocInstaller (as used for
  discovering the Bioconductor repositories active for the current project).
  BiocManager will be used for R >= 3.6.0; BiocInstaller will be used otherwise.

• The R option packrat.dependency.discovery.disabled can be set to TRUE to
  disable dependency discovery in projects. This can be useful if you find
  Packrat's dependency discovery is slow (as it can be in projects containing
  a large number of R Markdown files). (#513, @ras44)

• The scheme used for hashing packages that enter the Packrat cache has
  changed -- now, a defined ordering of fields is used when hashing a
  package's DESCRIPTION file. Note that this implies a package may need to be
  re-cached on restore, in the case that its hash has changed. This change
  should not affect any existing packages in the cache. (#505, @aronatkins)

• packrat::with_extlib() now works with no packages provided;
  both with and without this option, the new behavior is that expr
  is executed in an environment where the original (not packrat)
  library search path is in place.

• A project is now only considered 'packified' if it has both a Packrat
  lockfile as well as the associated autoloader in the project .Rprofile.

• Calling packrat::init() on a project that already contains a Packrat
  lockfile no longer attempts to re-snapshot and restore the project.

• Packrat now supports R packages available on BitBucket, courtesy of a PR from
  @mariamedp. (#481)

• Added the project option symlink.system.packages: users can now configure
  whether base R packages from the system library are symlinked into a private
  library packrat/lib-R. Disabling this can be useful if you intentionally
  want Packrat to use packages that have been installed into the system library.

• Fixed an issue where attempts to snapshot could fail when
  the R libraries live on a network drive.