Export stats to elasticsearch feature

Added a "plugin"-like structure for request/response analysis. 
(Analysis is done in separate go routines, so that the request rate doesn't get slowed down)
Added Timing information of the requests and responses.

Finally added an elasticsearch integration.

Request details can get exported into elasticsearch and are searchable in there.
The elasticsearch frontend Kibana3 (www.kibana.org) can visualize this data in nearly any way.