Base metrics

So there are several ways to make sure these go to Librato. I ended up copying this little layer from API because it's by far more lean and abstract than the options:

- Librato has their own gem, but it transmits via API calls as opposed to logs. This makes me nervous because I don't know how they're doing that reliably, without leaking memory, blocking, etc. Also not a fan of having a librato-specific dependency obviously.

- Some gems like [ruby-metrics](https://github.com/johnewart/ruby-metrics) support different backends, but none apparently transmits metrics via logs. This seems optimized for doing some aggregation locally, whereas for our web process we just want to fire and forget.