Calling ein:query-ipython-version with IPython 2.x running will result
in a request error since the api REST url is not implemented. Getting a
404 response is inevitable unless the IPython devs backport the api URL,
but I can make ein complain less when this happens.
BEWARE! This is a large commit and the code here is still mostly
untested. Back up your notebooks before giving this changeset a try with
the current IPython-dev version.
Given that, ein is now able to open and save basic notebooks saved in
nbformat 4. Still haven't tested more complex notebooks with embedded
images.
