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.


This suppose that the user understand (or have been told) the magic gets its parameter as string. Which is not obvious, and even contradictory with the fact that you said magics takes flags. I would either describe it receive argument as string, or just say that it does not need to be valid python.