! 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, 4 insertions, 4 deletions

diff --git a/kamon-newrelic/src/main/scala/kamon/newrelic/NewRelic.scala b/kamon-newrelic/src/main/scala/kamon/newrelic/NewRelic.scala
index c195ed12..85861454 100644
--- a/kamon-newrelic/src/main/scala/kamon/newrelic/NewRelic.scala
+++ b/kamon-newrelic/src/main/scala/kamon/newrelic/NewRelic.scala
@@ -18,8 +18,8 @@ package kamon.newrelic
 import akka.actor._
 import scala.concurrent.duration._
 import kamon.Kamon
-import kamon.metrics.{ CustomMetric, TickMetricSnapshotBuffer, TraceMetrics, Metrics }
-import kamon.metrics.Subscriptions.TickMetricSnapshot
+import kamon.metric.{ UserMetrics, TickMetricSnapshotBuffer, TraceMetrics, Metrics }
+import kamon.metric.Subscriptions.TickMetricSnapshot
 import akka.actor
 import java.util.concurrent.TimeUnit.MILLISECONDS
 
@@ -30,7 +30,7 @@ class NewRelicExtension(system: ExtendedActorSystem) extends Kamon.Extension {
   val apdexT: Double = config.getDuration("apdexT", MILLISECONDS) / 1E3 // scale to seconds.
 
   Kamon(Metrics)(system).subscribe(TraceMetrics, "*", metricsListener, permanently = true)
-  Kamon(Metrics)(system).subscribe(CustomMetric, "*", metricsListener, permanently = true)
+  //Kamon(Metrics)(system).subscribe(UserMetrics, "*", metricsListener, permanently = true)
 }
 
 class NewRelicMetricsListener extends Actor with ActorLogging {
@@ -50,7 +50,7 @@ object NewRelic extends ExtensionId[NewRelicExtension] with ExtensionIdProvider
   def createExtension(system: ExtendedActorSystem): NewRelicExtension = new NewRelicExtension(system)
 
   case class Metric(name: String, scope: Option[String], callCount: Long, total: Double, totalExclusive: Double,
-                    min: Double, max: Double, sumOfSquares: Double) {
+      min: Double, max: Double, sumOfSquares: Double) {
 
     def merge(that: Metric): Metric = {
       Metric(name, scope,