Clean up the simple-plot-cairo.py script some more.

This commit introduces the following changes:
- change the paper format to A4 for more convenient printing
- get the scaling right
- iterate over the shapes more efficiently
- remove some unused and unnecessary code
- make it clear that this script can be redistributed (under the
  terms of the GPL)
add my own ipython notebook
Merge pull request #2 from seehuhn/master

Clean up the simple-plot-cairo.py script some more.