Setup cache path
cache_setup(full_path = NULL, temp_dir = FALSE)
cache_info()(character) the full path to use for storing cached files.
(logical) if TRUE use a randomly assigned
tempdir (and full_path is ignored), if FALSE, you
can use full_path.
the full cache path, a directory (character)
On opening,  by default a temporary directory is created for caching
files.  To have files cached elsewhere,  give the full path of where to
cache files.  Adding temp_dir = TRUE will again use a temporary
dirctory for cacheing.
Other cache: 
cache_delete(),
cache_details(),
cache_list()
if (FALSE) {
# default path
cache_setup()
# you can define your own path
cache_setup(path = "foobar")
# set a tempdir - better for programming with to avoid prompt
cache_setup(temp_dir = TRUE)
# cache info
cache_info()
}