Add fields to context wrapper

[massover]

This adds meta, user, and comment support to the _ContextWrapper.

I found it nice to build/test my own create_revision.

def create_revision_for_obj(user, manage_manually=False, using=None, atomic=True, **kwargs):
    from reversion.models import Revision
    using = using or router.db_for_write(Revision)
    return _ContextWrapper(_create_revision_context, (manage_manually, using, atomic), ObjMeta, user, **kwargs)

I then could use it like so (as user and the meta obj were always required):

meta_values = {'hello': 'world'}
with create_revision_for_obj(request.user, **meta_values):
  obj.save()

Compared to this:

meta_values = {'hello': 'world'}
with create_revision():
  add_meta(ObjMeta, **meta_values)
  set_user(request.user)
  obj.save()

I'm not particularly attached to modifying the actual create_revision from the library. But I did add that in case that change to the api was liked. This is more about the changes to _ContextWrapper to build your own create_revision context managers. I am glad to remove it.

[etianen]

Nice idea!

I think that this should be implemented inside the _create_revision_context function, since then the calls to set_meta, set_comment etc only need to be implemeted in one place.

[massover]

@etianen that was a great suggestion!

I moved the code to _create_revision_context. I actually removed the changes from create_revision as to not touch that since I don't need it. I also added an arguably useless test in another commit so it can be removed easily if you prefer to not keep it. Let me know if you think there is any documentation to add for this.

[etianen]

Thanks!

Any chance of a pull request to update the docs: https://github.com/etianen/django-reversion/tree/master/docs ?

[etianen]

Unfortunately, I've had to revert this pull request.
Extra fields should be added to create_revision(), not _create_revision_context(), which is a private API.