The rationnal to do this migration are:

* be able to host the documentation on readthedocs.org, right now, according to
  the README, the user needs to built it locally to be able to read it
* epydoc is not maintained anymore
* sphinx generally offer a better user experience and allow to write real
  documentation instead of just generating an API
* it was quick to do with sphinx-apidoc and seems worth it to be able to put it
  online