Fix a little issue I noticed in the install guide

The ipythonprinting extension is deprecated in favor of init_printing().
Fix the release fabfile for the single Python 2/3 codebase

I believe it works (it seems to work off a branch on my fork).

Note, to test this, you'll need to comment out the mailmap_update line in the
release() function as the .mailmap file hasn't been updated yet.