Tutorial for writing a JSON river which streams data into elasticsearch

This howto shows the reader how to implement a JSON river, which streams the data into elasticsearch and uses bulk requests in order to index data.

The river has support for deleting data as well, has mechanisms for ensuring the river does not cause OOM exceptions and is generally easy to use.

This document should help end users to implement their own river implementations instead of being the one river everyone should use (this will and should never happen in a dynamic JSON world).