added parm type checking; minor bugfix (nrows for vector pnts input); added name-to-id conversion on fids
fields_description_to_id renamed to fields_name_to_id; reverse function fields_id_to_name added
changed "fields" references to "layers"; added use_layer_names and (as-yet undocumented) ability to supply layers as names instead of ids
added rename_variables to utilities
added dots to param docs