Add Fluentd, Ruby-based log aggregation daemon

Fluentd is an open-source log aggregation daemon, written by Ruby.

- Source: http://github.com/fluent/fluentd/
- Document: http://fluentd.org/
- Fluentd: the missing log collector ( http://bit.ly/rLdzn6 )

Compared to Facebook's Scribe logging daemon, these points are the benefit (@see http://bit.ly/yQBC0J).

- Easy Installation
- Small Footprint
- Semi-Structured Data Logging
- Flexible Plugin Mechanism
- Reliable Buffering
- Log Forwarding

The some of existing users are introduced on Quora ( http://www.quora.com/Who-uses-Fluentd-in-production ).

Could you add Fluentd to this repository? Thanks - K