Major rewrite of notebook based documentation/examples

This is the beginning of a major rewrite of the notebook based documentation and examples that are in /examples and hosted on nbviewer. Some of the goals of this PR:

* Remove duplicate content between here at our ipython-in-depth repo where we have tutorials. This involves separation out narrative documentation from more tutorial style content (mainly exercises).
* /examples in this repo is considered the master location of our narrative/tutorial content. For now, we have  fabric scripts in ipython-in-depth that copies over the relevant content to ipython-in-depth by hand.
* Reorganize this content into better conceptual categories and are reflected in a top-level directory structure and notebook names.
* Move Python specific stuff out of the "IPython Notebook" category into the "IPython Kernel" category, so that our notebook related docs are more-or-less language neutral.
* Begin to move certain parts of our sphinx docs over to notebooks.


In this context, `display` seem useless as people do not understand that all result computed are stored. I would emphases that `display_png` should only be use in specific cases.