Release v0.5 to PyPI

Thanks for this great project! However, when I did `pip install ipynb` I got version 0.4, which does not correctly comment out markdown cells when converting into code (fixed in commit b266e352bf1726477129270d4530ed2df7bdc580, which lies between 0.4 and 0.5). Currently one must do `pip install -e git+https://github.com/ipython/ipynb#egg=ipynb` to get the fixed version.

NB, the PyPI page also has an old project URL http://github.com/yuvipanda/ipynb instead of http://github.com/ipython/ipynb .

Start by reviewing commit b266e352bf1726479270d4530ed2df7bdc580 and the project's current package release configuration. Publish the fixed v0.5 package to PyPI, update the PyPI project URL to the ipython repository, and verify that pip install ipynb retrieves the corrected version.

Escrito por el modelo de indexación a partir del texto del issue.