[doc] more fixes of warnings/errors in doc build
- move 3.21.rst changelog description at it's proper place
- include changelogs in the main index
- few typos
- add :noindex: for autoxxx directives not in api/
Related to #4832808
.. _rset_module:
:mod:`cubicweb.rset`
====================
.. automodule:: cubicweb.rset
.. autoclass:: ResultSet
:members: