regional_output: A list of output as produced by regional_epinow()
and stored in the regional list.
target_folder: Character string specifying where to save results (will create if not present).
target_date: A character string giving the target date for which to extract results (in the format "yyyy-mm-dd"). Defaults to latest available estimates.
return_output: Logical, defaults to FALSE. Should output be returned, this automatically updates to TRUE if no directory for saving is specified.