Feature/responsible shard (#294)

* getResponsibleShard

* changelog upd

* doc upd

Author: rashtao

ChangeLog.md

@@ -8,6 +8,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/) a
 
 ### Added
 
+- added `ArangoCollection#getResponsibleShard(Object)`
 - added support for Analyzers
 - added support for Stream Transactions
 - added support for named indices