Add additional utility functions and second core function, then write tests

[drkennetz]

For people learning, write additional utility functions, add a second core function, and write tests.

[drkennetz]

There are multiple ways to handle this. We could either create separate branches for more in depth tests or restructure the directories to have an increasing level of testing difficulty.. An example would be:

./py_unittest_walkthrough
  ./getting_started
    ./bin
    ./src/funprog
    ./test
  ./argparse_unittests
    ./bin
    ./src/argparse_fun
    ./test
  ./class_testing
    ./bin
    ./src/class_testing
    ./test
...

Where each directory contains a testing suite. I prefer using directories rather than branches but this would need to be reflected in the README. Thoughts @rjbeers @xanderyzwich

[xanderyzwich]

I'd prefer the directory approach as I believe it would be more intuitive to 'users'