Add further tests for unanticipated edge cases

I found some further examples of tries - which broke my code.

This release includes a fixs for the new edge case.

Refactored tests

Cleaned up and refactored tests to make them more extensive & extensible in preparation for further work.

Working but not ready for prime time

I missed the session where this project was selected,
so I'm not completely clear on what Patricia tries are
actually good for.

Even so, it was an excellent learning exercise.

I've since done some research, which meant extra
edge cases which I have yet to write code to handle.