[Contribute] Include the Makefile, the conf.py and the sensio's sphinx extension to make testing easier.

[wouterj]

:+1:

This will also enable the possibility to use Travis on this repo. On the CMF docs, we enabled travis last week and I'm pretty happy with it. Travis will parse the docs using sphinx and then report any errors. That means we solve all sphinx error when a PR is opened, instead of after it.

I propose to create a pip package for fabpot's sphinx extensions, we shouldn't duplicate code here from that repo. /cc @fabpot

I actually don't know how this will work out for the online docs, @fabpot ?

And @weaverryan I would like to get your opinion about this and Travis. You can see an example in the PRs in symfony-cmf/symfony-cmf-docs

EDIT: pupet -> pip

[docteurklein]

based on docs, we could use git submodules too, and script travis like that:

language: python

python:
    - "2.7"

install: "git submodule update --init"

script: make html

See http://sphinx-doc.org/extensions.html#where-to-put-your-own-extensions