[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.

Data model
==========

This chapter describes how you define a schema and how to make it evolves as the time goes.

.. toctree::
   :maxdepth: 1

   definition
   metadata
   baseschema
   define-workflows