Add a backend to librato.com

[lukevenediger]

As a librato.com customer with a Windows-based infrastructure I would like to a windows-based collector and output the aggregated data to my librato.com account.

See https://github.com/librato/statsd-librato-backend for configuration options and reference.

[phillijw]

The sourceRegex feature would be particularly useful for my use case where we have one statsd service that multiple machines are connecting to. For now, I'm going to run one statsd instance on each machine instead but this would prove to be useful in the future.