Settings only read once. Added manager. Corrected iterator. Added tests.

+ Settings only read once
 * Moved any setting reading to the _static block_ of `Bungiesearch`.
 * Renamed `bungiesearch.Search` to `bungiesearch.Bungiesearch` to avoid naming conflicts with `elasticsearch-dsl-py`.

+ Added Django manager:
 * It is now possible to use Bungiesearch as a manager. An example is in tests/core/models.py and in tests/test_model_index.py .

+ Corrected iterator:
 * Iteration will now execute the query, e.g. `[result for result in Article.objects.search.query('match', title='title')]` executes the query before iterating, and so does `list(Article.objects.search.query('match', title='title'))` .
+ Added tests:
 * Create, update and delete index (done at every test run).
 * Search testing: searches on the index for both items independently and together.