Aspell based spellchecker

Simple aspell-based server-side spell checker. The notebook extension communicates with aspell using a websocket connection. Provides live spell checking in non-code cells and on-demand for any celltype.

Requires `aspell` and `aspell-python` installed, and `ipy-aspell.py` running on Linux.

See: http://www.youtube.com/watch?v=yk5ID5SAlLw