Harmonized expanded thw-functions modules

The bc repository currently contains two versions of the thw-funcitons-modules ipython notebook lesson:

`lessons/thw-python/functions-modules/python_functions_and_modules.ipynb`     --the older lesson
`lessons/thw-python/functions-and-modules/python_functions_and_modules.ipynb`  --an expansion of the lesson by @scopatz with more explicit syntax, slower introduction, and explication on keyword arguments, unpacking return values, function decorators, and  lambda functions.

This PR moves typographical edits to the expanded version and moves the elementary exposition on what functions are to the smaller.    

The keyword arguments, return values, decorators, and lambda functions I suspect are suitable for some audiences but not others, but the explicit function-definition syntax reference is a clear improvement that doesn't change the scope of the lesson.