[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
The 'download' views
====================
.. automodule:: cubicweb.web.views.idownloadable
Components
----------
.. autoclass:: cubicweb.web.views.idownloadable.DownloadBox
Download views
--------------
.. autoclass:: cubicweb.web.views.idownloadable.DownloadView
.. autoclass:: cubicweb.web.views.idownloadable.DownloadLinkView
.. autoclass:: cubicweb.web.views.idownloadable.IDownloadablePrimaryView
Embedded views
--------------
.. autoclass:: cubicweb.web.views.idownloadable.ImageView
.. autoclass:: cubicweb.web.views.idownloadable.EHTMLView