! all: refactor the core metric recording instruments and accomodate UserMetrics

This PR is including several changes to the kamon-core, most notably:
  - Formalize the interface for Histograms, Counters and MinMaxCounters. Making sure
    that the interfaces are as clean as possible.
  - Move away from the all Vector[Measurement] based Histogram snapshot to a new approach
    in which we use a single long to store both the index in the counts array and the
    frequency on that bucket. The leftmost 2 bytes of each long are used for storing the
    counts array index and the remaining 6 bytes are used for the actual count, and
    everything is put into a simple long array. This way only the buckets that actually
    have values will be included in the snapshot with the smallest possible memory
    footprint.
  - Introduce Gauges.
  - Reorganize the instrumentation for Akka and Scala and rewrite most of the tests
    of this components to avoid going through the subscription protocol to test.
  - Introduce trace tests and fixes on various tests.
  - Necessary changes on new relic, datadog and statsd modules to compile with the new
    codebase.

Pending:
  - Finish the upgrade of the new relic to the current model.
  - Introduce proper limit checks for histograms to ensure that we never pass the 2/6 bytes
    limits.
  - More testing, more testing, more testing.
  - Create the KamonStandalone module.

1 files changed, 2 insertions, 5 deletions

diff --git a/kamon-playground/src/main/scala/test/SimpleRequestProcessor.scala b/kamon-playground/src/main/scala/test/SimpleRequestProcessor.scala
index 664bd4f9..84621927 100644
--- a/kamon-playground/src/main/scala/test/SimpleRequestProcessor.scala
+++ b/kamon-playground/src/main/scala/test/SimpleRequestProcessor.scala
@@ -26,9 +26,9 @@ import scala.util.Random
 import akka.routing.RoundRobinPool
 import kamon.trace.TraceRecorder
 import kamon.Kamon
-import kamon.metrics._
+import kamon.metric._
 import spray.http.{ StatusCodes, Uri }
-import kamon.metrics.Subscriptions.TickMetricSnapshot
+import kamon.metric.Subscriptions.TickMetricSnapshot
 
 object SimpleRequestProcessor extends App with SimpleRoutingApp with RequestBuilding with KamonTraceDirectives {
   import scala.concurrent.duration._
@@ -55,8 +55,6 @@ object SimpleRequestProcessor extends App with SimpleRoutingApp with RequestBuil
   val replier = system.actorOf(Props[Replier].withRouter(RoundRobinPool(nrOfInstances = 2)), "replier")
   val random = new Random()
 
-  val requestCountRecorder = Kamon(Metrics).register(CustomMetric("GetCount"), CustomMetric.histogram(10, 3, Scale.Unit))
-
   startServer(interface = "localhost", port = 9090) {
     get {
       path("test") {
@@ -87,7 +85,6 @@ object SimpleRequestProcessor extends App with SimpleRoutingApp with RequestBuil
         path("ok") {
           traceName("OK") {
             complete {
-              requestCountRecorder.map(_.record(1))
               "ok"
             }
           }