Automated testing, documentation, refactoring.

edited: word_pattern simplified while providing the same functionality.
added: TEXT_FIXTURES to store sample data to be tested.
added: docstring automated unit tests and as documentation.
  now you can run 'python -m doctest Araby_Statistics.py' and
  if all goes well it well display nothing, while if any test fails,
  it will display the test and the expected value and the actual value.
edited: all 'print \<expr\>' are now 'print( \<expr\> )' for compatibility with python3.