Execute ipynb and write a nbconverted html...

The idea here is to test a simple ipynb to see if it is rendering OK when it is nbconverted, and then if it would be nbviewer-ed OK.
I am using a custom script to execute and nbconvert the notebook, in the future we could change this for a `IPython.nbconvert` preprocessor currently in PR state, but not available until IPython 3.0 
Maybe easier to specify the ones you don't want to skip, i.e. `include_travis`? That could be a later enhancement though.