building docs under Python 3 after ipython_directive merge
As requested in [#5530 (comment)] and after the merge of #5925, I am trying to test building the docs on python 3. I get the error:

```
Traceback (most recent call last):
  File "/Users/user/.virtualenvs/pandas-dev/lib/python3.3/site-packages/sphinx/cmdline.py", line 245, in main
    warningiserror, tags, verbosity, parallel)
  File "/Users/user/.virtualenvs/pandas-dev/lib/python3.3/site-packages/sphinx/application.py", line 119, in __init__
    self.setup_extension(extension)
  File "/Users/user/.virtualenvs/pandas-dev/lib/python3.3/site-packages/sphinx/application.py", line 283, in setup_extension
    mod = __import__(extension, None, None, ['setup'])
  File "/Users/user/Optional/pandas-phaebz/doc/sphinxext/numpydoc.py", line 40
    title_re = re.compile(ur'^\s*[#*=]{4,}\n[a-z0-9 -]+\n[#*=]{4,}\s*',
SyntaxError: invalid syntax
```

I thought about it and talked to @kermit666: where should this be taken care of? 
