Documentation fails to build with Python 3

Documentation fails to build with Python 3.
```
$ python3.3 make.py
Running Sphinx v1.2b1

Exception occurred:
  File "conf.py", line 47, in <module>
    if sphinx.__version__ >= 1.1:
TypeError: unorderable types: str() >= float()
...
```

Patch:
```
--- doc/conf.py
+++ doc/conf.py
@@ -44,7 +44,7 @@
 
 autosummary_generate = True
 
-if sphinx.__version__ >= 1.1:
+if sphinx.__version__ >= '1.1':
     autodoc_docstring_signature = True
 
 # Add any paths that contain templates here, relative to this directory.
```