replacement for argparse with config files and environment variables (Python 3)

 Applications with more than a handful of user-settable options are best
 configured through a combination of command line args, config files,
 hard-coded defaults, and in some cases, environment variables.
 .
 Python’s command line parsing modules such as argparse have very limited
 support for config files and environment variables, so this module extends
 argparse to add these features.
 .
 This is the Python 3 module.