Steve Witham's Twitter Puddle solutions (fixed)

Hi,

(Previously made and closed a pull request with a missing commit.)

This contains an iiPython notebook and a png illustration.
The link in index.html is to a URL at [http://nbviewer.ipython.org], which then links to the copy of the notebook in my fork of the github repo. The link to the illustration within the notebook is also to my fork.

I think thiat's all okay as is. People will by default be directed to my copies, but I will keep them around, plus there will be good copies in the [https://github.com/BostonPython/puzzles] repo also.

But, it is also okay with me if you want to point those links into the BostonPython repo.

--Steve