fix check_if_function, non-const-globals, closes #19, closes #16
Update README.md
Update README.md
Returned success code from regression_test.py.

So now I can add a pre-commit hook that won't let me commit broken code,
which I couldn't do before. That is:

    #!/bin/bash
    source .venv/bin/activate
    python regression_test.py
Update README.md
remove more pyparsing, closes #6, closes #20