Remove ipython_notebooks directory

[wtbarnes]

The ipython_notebooks directory should be removed. The examples in the quickstart notebook should be moved to the docs, perhaps rendered with sphinx gallery. See also #145

[kdere]

It should be put in a place where users will find it most easily. The docs directory would be fine but I have also seen examples where the notebook directory is on the same level as the docs directory. Neither astropy or sunpy seem to have notebooks so they don't provide any precedence.