When activated, dev_mode creates a new library for storing installed
packages. This new library is automatically created when dev_mode is
activated if it does not already exist.
This allows you to test development packages in a sandbox, without
interfering with the other packages you have installed.
dev_mode(on = NULL, path = getOption("devtools.path"))turn dev mode on (TRUE) or off (FALSE). If omitted
will guess based on whether or not path is in
.libPaths()
directory to library.
if (FALSE) { # \dontrun{
dev_mode()
dev_mode()
} # }