Pass full document to block since _source may not be present

* It is common for queries to explicitly disable return of the document _source
* See http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/search-request-source-filtering.html
Update readme to show doc returned with _source
Merge pull request #1 from evertrue/andrew/doc-source

Pass full document to block since _source may not be present