Add function call stack diagrams to Python functions notebook.

I added 1 stack frame diagram below those for which there were `FIXME` placeholders. It brings the illustration of the `body_temp_f` calculation back to the base stack frame that it started from.

The visual vocabulary is inspired by Ned Batchelder's [Python Names and Values](http://nedbatchelder.com/text/names.html) blog post, and is used with his permission.