+ spray-metrics, spray-routing: Integrating Coda Hale Metrics

- Added Directives for counters, meters and timers
- Metrics can be given specific names or have their names calculated dynamically
  based on the route and method (e.g. path.to.object.GET)
- Many of the metrics directives are helped by the addition of the `around`
  directive, which was added to the BasicDirectives object
  - You provide functions that execute before and after the surrounded route
    executes