types and parsers for epoch time and absolute DateTime


figured out how to do heterogenous lists with json4s.

```scala
import org.json4s._
import org.json4s.native.Serialization
import org.json4s.native.Serialization.{read, write}

case class GraphiteOutput(target: String, datapoints: Array[Array[Any]])

implicit val formats = DefaultFormats
def render(name: String, data: Seq[(Long,Double)]): String = {
  def f(xs: Seq[(Long,Double)]): Array[Array[Any]] = xs.map(p => Array[Any](p._2,p._1)).toArray
  write(Array(GraphiteOutput(name, f(data))))
}
```
it produces:

`[{"target":"test0","datapoints":[[4.787332364925626,1415190499],[6.857665240740156,1415190500]...`