Enhance documentation

I added the undoc members to the documentation to fix #46. While I was in the mood, I added links the the official python documentation using the [intersphinx sphinx extension](http://sphinx-doc.org/ext/intersphinx.html).

Links could be added using [`.. seealso::` blocks](http://sphinx-doc.org/markup/para.html#directive-seealso) but they are bigger. What do you prefer ?

To build the documentation, I had to remove the `html_static_path` in `conf.py`, is it a bug or I did something wrong ?