Check doctests

[volcan01010]

Summary

As a BNG.py developer, I want to use doctests to ensure that the documentation is correct.

Description

Doctests run Python code given as examples in docstrings and confirms that the results are as expected.

https://docs.python.org/3/library/doctest.html

BNG has such code in the docstrings, but the tests have never been tried.

Acceptance

• Add if '__name__' == '__main__' section to allow easy running of doctests
• Confirm that doctests all pass