[doc] Restructure the documentation
* Create a new index file
* Move the sphinx configuration files do the documentation root
* Move book/README to dev/documenting.rst
* Move book/mode_plan.py to tools/
* Move book/en/images to images
* Move book/en/* to book/
* Move changelogs to changes/*
* Adapt the Makefile
* Add a title to the javascript api index
Related to #4832808
Startup views
-------------
Startup views are views requiring no context, from which you usually start
browsing (for instance the index page). The usual selectors are
:class:`~cubicweb.predicates.none_rset` or :class:`~logilab.common.registry.yes`.
You'll find here a description of startup views provided by the framework.
.. automodule:: cubicweb.web.views.startup
Other startup views:
*schema*
A view dedicated to the display of the schema of the instance
.. XXX to be continued