This allows users to log outgoing documents before they are sent.
This may break backwards compatibility by changing the arity of on_before_dispatch, but we couldn't get the tests to run via rake test so we're unsure of how to test that we're not breaking every existing implementation.
Pass `doc` to `on_before_dispatch`
Makes sense why you'd want this. I guess the BC is acceptable here - Breakage will be trivial to fix.