dependencies: logical indicating to also install uninstalled packages
which these packages depend on/link to/import/suggest (and so
on recursively). Not used if ‘repos = NULL’. Can also be a
character vector, a subset of ‘c("Depends", "Imports",
"LinkingTo", "Suggests", "Enhances")’.
Only supported if ‘lib’ is of length one (or missing), so it
is unambiguous where to install the dependent packages. If
this is not the case it is ignored, with a warning.
The default, ‘NA’, means ‘c("Depends", "Imports",
"LinkingTo")’.
‘TRUE’ means (as from R 2.15.0) to use ‘c("Depends",
"Imports", "LinkingTo", "Suggests")’ for ‘pkgs’ and
‘c("Depends", "Imports", "LinkingTo")’ for added
dependencies: this installs all the packages needed to run
‘pkgs’, their examples, tests and vignettes (if the package
author specified them correctly).