[doc] fix warnings/errors in doc build
- fix links to images
- fix a couple of typos
- re-add IDownloadableOneLineView doc
- rename documenting.rst back to .txt, it's intended as a doc of how to
write rst, not part of the rst doc
Related to #4832808
.. _Part2:
----------------------
Repository development
----------------------
This part is about developing applications with the *CubicWeb*
framework. It is not concerned with the web system, which is a
separate layer and has its own whole chapter.
.. toctree::
:maxdepth: 2
:numbered:
cubes/index
vreg.rst
datamodel/index
entityclasses/index
devcore/index
repo/index
testing.rst
migration.rst
profiling.rst
fti.rst
dataimport