pep8 fixes
Default manager should never return unapproved objects

Since there is no explicit field in ModeratedObject that stores whether the
object has ever been approved, use the moderation_date field which is always set
when an object is approved.
Post moderation signal should send the updated instance.
Merge pull request #89 from sahilgupta/fix_moderation_signal

Post moderation signal should send the updated instance. Thank you @sahilgupta good job!
Merge pull request #86 from adityar7/master

Default manager should never return unapproved objects
Add a failing test for the changed_by property

the changed_by property is not set on staff admin saving
Improve the failing test

since it was using the default generic moderator on Book, the
`auto_approve_for_staff` was set to `True` and the test was not failing
like it should have been
Fix the `changed_by` property affectation

little explanation why : if `auto_approve_for_staff` is set to False
then `save` is never called on the moderated object because the status
is neither approved or rejected. so we prefer explicit call in every
case
Make pep8 tests pass
Merge pull request #91 from dulaccc/fix-changed-by-not-set

Fix the `changed_by` property not set. Thank you @dulaccc Good job!
Merge pull request #92 from dulaccc/master

Add travis build status to README