Added IPython Notebook with code and plots from your slides

Hey Mel! 

I added two files: (1) the flute.wav file, to make access to it easier, and (2) an IPython Notebook (.ipynb file) with the code and plots from your slides (the notebook needs the .wav file to work).

You can preview the notebook here: http://nbviewer.ipython.org/github/amygdalama/pycon-sigproc/blob/master/signal_processing.ipynb

To interactively execute the code in the notebook, you'll need IPython installed on your computer. Once you get that set up, in the terminal navigate to the directory housing the .ipynb file and type `ipython notebook`. Then a tab should open in your browser with the code! You can press shift+enter in any cell to execute the code in that cell. To execute all of the code at once, you can go to Cell > Run All in the top menu.