MultiSearch implementation
Fixed empty query issue
More multi search tests
Added support for error response in multi search
Extracted elasticsearch version into env var
Added 5.2, 5.3 and 5.4 php version to travis.yml
Added setSearchType method in Elastica_Multi_Search
Added createSearch method to Type and Index. Count request is preformed by calling Elastica_Search::count() method
Merge master branch into munkie-multi-search