move image to subdirectory
description of the image subdirectory
Adding numpy notebooks, conversion still a bit rough

Converted from:

https://github.com/esc/scipy-lecture-notes/commit/1845014477ec13b319dc559e02c080afe27fe530

Converted by:

https://github.com/esc/nbconvert/commit/1df8c2b8a5daad75516af1bd7d3f647ea387cacd

And using the docutils patch from:

http://permalink.gmane.org/gmane.text.docutils.user/7047