Support for search_type query string param to searches.

Conflicts:
	elasticutils/__init__.py
Fix cloning S with search_type, add tests
Change search_type to be a chainable method
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Explicitly ask Elasticsearch for two shards

At least two shards are necessary for testing query_and_fetch search
type. Make sure that even if the global ES configuration only specifies
one shard, the test still works.
Expand the documentation
Merge pull request #186 from infoxchange/search_type

Search type support