jupyter-sphinx backwards-incompatible update

[akhmerov]

This project uses jupyter-sphinx for building documentation. We have just rewritten jupyter-sphinx from scratch, and fully changed the interface.

Now all code execution is done via a single jupyter-execute sphinx directive, instead of the previous ipywidgets-setup/ipywidgets-embed.
The new version is also much more flexible: it allows to embed any output recognized by jupyter in sphinx documentation.

We have released 0.2.0rc1 on pip, please give it a shot using pip install 0.2.0rc1 --pre — we would love to hear your feedback.
In case you do not plan to upgrade in the near future, pin the version 0.1.4 for building the documentation.
Please also let us know by responding here or in jupyter/jupyter-sphinx#33 if the new release disrupts your workflow.