py-environ: ConfigParser with environmental override

This is a ConfigParser implementation that forwards to SafeConfigParser to load and parse configuration, while allowing option values to be overriden from the environment.

Usage

    from py_environ import EnvironmentConfigWrapper

    # Create a config parser
    config = EnvironmentConfigWrapper()
    
    # Use as is
    option_one_str = config.get('My Section', 'option_one')
    option_two_int = config.getint('My Section', 'option_two)
    
    # In this case, the option value in the ConfigParser is overridden
    # by the environment variable MY_SECTION_OPTION_THREE
    option_three = config.get('My Section', 'option_three')