[collectd] Native output plugin for Graphite

[Scott Sanders]

Hi everyone,

I was interested in visualizing metrics from a group of collectd nodes
in graphite and decided to create an output plugin for collectd in C
to handle this task. The plugin is based heavily on the existing
write_http plugin.

If you think this may be useful, please grab a copy from
https://github.com/jssjr/collectd-write_graphite and let me know what
you think. I'm using the plugin successfully on a fair number of
production hosts without any issues. Any testing and feedback the
community can provide would be greatly appreciated.

Some improvements I intend to make in the short term:
- Queue send buffer if flush is called but Carbon host isn't available
- Derive metrics before sending to Carbon depending on type

Thanks!

-Scott Sanders