Track authors on Editable objects

[noyainrain]

Introduce Editable.authors which tracks users who edited (or created) an object.

Depends on #4 .

[noyainrain]

Draft:

class Editable:
    """
    .. describe:: authors

       :ref:`User` s who edited the object.

    --
    The :meth:`Object.json` method of editable objects accepts an additional argument
    *include_users*. If it is ``True``, :class:`User` s are included as JSON objects (instead of
    IDs).
    """

    def do_edit():
        """
        Called by :meth:`edit`, which takes care of basic permission checking, managing *authors*
        and storing the updated object in the database.
        """

    def json(self, include_users=False):
        """
        Subclass API: Return a JSON object representation of the Editable part of the object.
        """

[noyainrain]

Implemented in ff1511e795d432a0504f105874bff5425215a5e6 .