Added option to enable/disable "_source" field on search requests.
(http://www.elasticsearch.org/guide/en/elasticsearch/reference/master/search-request-source-filtering.html)
Enabled option to store Field Types different than StringType under Multi Fields.
(http://www.elasticsearch.org/guide/en/elasticsearch/reference/0.90/mapping-multi-field-type.html#mapping-multi-field-type)