'recursive_copy' helper function changed from public to private
'recursive_delete' helper function added. It will be used by the new 'delete' action.
'check_source_exists' helper function added. It checks the existense of the source_file parameter and the existence of the file pointed by this parameter.
'check_target_exists' helper function added. It checks the existence of the target_file parameter and create the required directory.
'command' function fully restructured. All actions moved to a new switch/case structure.
'delete' action added. It uses the new 'remove_file' parameter (and doesn't require the source_file and target_file parameters).