First attempt at blueflood output

This output lets you pull metrics from your logs and emit them to your Blueflood endpoint. 
 
Blueflood (http://blueflood.io) is a distributed, multi-tenant metrics processing solution, created by engineers at Rackspace Blueflood is capable of ingesting, rolling up and serving metrics at a massive scale. 

The metrics can either be sent as well-formed JSON  (examples: https://github.com/rackerlabs/blueflood/wiki/10minuteguide) or as a hash. 

Sample use case: You are logging the load average of your system every 30 seconds. Using a grok filter and the Blueflood output plugin, you can send these metrics to Blueflood. See many such examples in our sample logstash conf files here https://github.com/rackerlabs/blueflood/tree/master/contrib/logstash-blueflood

Looking forward to your reviews and comments!