add function scroll

function scroll ist the same as scan but with order the results (http://www.elasticsearch.org/guide/en/elasticsearch/guide/current/_sorting.html)
the scan function ignore ordering/sorting (http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/search-request-scroll.html#scroll-scan).

...  with the scan search type to disable sorting and to return results in the most efficient way ....

if you need sorting this function will help to scroll over the data.