[schema] use json to serialize constraints
Require yams 0.43: constraints are serialized to json, which means we
need to recreate the actual checks in the database on upgrade.
Temporary deps in tox.ini to pull respective changes in yams.
.. _rset_module:
:mod:`cubicweb.rset`
====================
.. automodule:: cubicweb.rset
.. autoclass:: ResultSet
:members: