Add python3 doc building capability

```
build succeeded, 85 warnings.
cp -r source/plots build/html

Build finished. The HTML pages are in build/html.
```


![screenshot from 2014-12-13 12 00 38](https://cloud.githubusercontent.com/assets/2096628/5424670/b23b673c-82bf-11e4-949a-f1fe636d3bd3.png)