Sets (if create = TRUE) or gets the cache
directory associated with the Require package.
RequireCacheDir(create)RequirePkgCacheDir(create)
If !is.null(getOptionRPackageCache()), i.e., a cache path exists,
the cache directory will be created,
with a README placed in the folder. Otherwise, this function will just
return the path of what the cache directory would be.
A logical indicating whether the path should
be created if it does not exist. Default is FALSE.
To set a different directory than the default, set the system variable:
R_USER_CACHE_DIR = "somePath" and/or R_REQUIRE_PKG_CACHE = "somePath"
e.g., in .Renviron file or Sys.setenv(). See Note below.