Allow bulk actions to have routing

The elasticsearch bulk API allows for each item to have a routing value
which helps prevent bulk actions from being broadcast to all shards.

http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/docs-bulk.html#bulk-routing
Allow the passing of a routing value for `deleteIds()`

If all ids to be deleted during a bulk API request are routed to the same
shard allow that routing value to be set so that the delete command is not
broadcast to all shards.
Update changes doc
Code cleanup
Merge pull request #631 from xyu/route-bulk-actions

Allow routing of bulk API actions