separate bind/publish host in flags/config

Its fairly common for servers to let you configure 2 separate addresses, a bind host and a publish host.

Here is the relevant section of the Elasticsearch docs: https://www.elastic.co/guide/en/elasticsearch/reference/1.6/modules-network.html

Came from #97

Start by reviewing the originating issue #97 and the linked Elasticsearch network documentation. Identify how flags/config currently represent server addresses; done means bind and publish hosts can be configured independently, with their behavior documented and verified.

Written by the indexing model from the issue text.