These functions turn caching of data files (and reading from cache) on/off in all subsequent isoread calls by changing the global settings for the
cache parameter. Can be called stand alone or within a pipeline.
iso_turn_reader_caching_on(data = NULL) iso_turn_reader_caching_off(data = NULL)
a data frame - returned invisibly as is if provided (e.g. in the middle of a pipeline)