write_blueflood: added Blueflood plugin

Added write_blueflood plugin that can send metrics to Blueflood HTTP 2.0 interface
See http://blueflood.io/
Example configuration can be found in collectd.conf.pkg-orig
Merge pull request #1 from pkit/write_blueflood

write_blueflood: added Blueflood plugin