Deprecate river
Deprecate river

**Rivers are [deprecated](https://www.elastic.co/blog/deprecating_rivers) and will be removed in the future.**
Have a look at [logstash twitter input](http://www.elastic.co/guide/en/logstash/current/plugins-inputs-twitter.html).

Closes  #104.

elastic/elasticsearch-river-twitter,elastic/elasticsearch-river-twitter