Flesh out slicing docs
Issue 102. Fix django tasks code

This fixes the elasticutils.contrib.django.tasks code, updates the
docs, and adds tests so if it fails in the future, I'll know.
Update CHANGELOG
Add warning about index_objects and chunking
Issue 104. Fix ElasticSearchTestCase

This updates the ElasticSearchTestCase code, makes it better, and
updates the documentation.
Fix goof in tests

We had two tests with the same name. This fixes that.
Issue 55. Add .all()

* add .all()
* update docs for .count(), .execute(), .__len__(), and .__iter__()
* add tests for things, too
Update CHANGELOG
Add missing space in docs
Added ES error middleware for Django (issue #47)