Add variable labels and rename to human readable column names
Arguments
- pumf_data
- pumf data file 
- pumf_base_path
- optional base path, guessed from attributes on - pumf_data
- layout_mask
- optional layout mask in case there are several layout files, guessed from attributes on - layout_mask
- rename_columns
- rename PUMF columns to human readable names, default is `TRUE` 
- infer_missing_numeric
- optional character, infer variables that aren't labelled to be numeric