! 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.

2 files changed, 5 insertions, 6 deletions

diff --git a/kamon-play/src/main/scala/kamon/play/instrumentation/WSInstrumentation.scala b/kamon-play/src/main/scala/kamon/play/instrumentation/WSInstrumentation.scala
index 0951d2c9..2862ba19 100644
--- a/kamon-play/src/main/scala/kamon/play/instrumentation/WSInstrumentation.scala
+++ b/kamon-play/src/main/scala/kamon/play/instrumentation/WSInstrumentation.scala
@@ -19,7 +19,7 @@ package kamon.play.instrumentation
 import org.aspectj.lang.annotation.{ Around, Pointcut, Aspect }
 import org.aspectj.lang.ProceedingJoinPoint
 import kamon.trace.TraceRecorder
-import kamon.metrics.TraceMetrics.HttpClientRequest
+import kamon.metric.TraceMetrics.HttpClientRequest
 import play.api.libs.ws.WSRequest
 import scala.concurrent.Future
 import play.api.libs.ws.WSResponse
@@ -36,7 +36,7 @@ class WSInstrumentation {
   def aroundExecuteRequest(pjp: ProceedingJoinPoint, request: WSRequest): Any = {
     import WSInstrumentation._
 
-    val completionHandle = TraceRecorder.startSegment(HttpClientRequest(request.url, UserTime), basicRequestAttributes(request))
+    val completionHandle = TraceRecorder.startSegment(HttpClientRequest(request.url), basicRequestAttributes(request))
 
     val response = pjp.proceed().asInstanceOf[Future[WSResponse]]
 
@@ -50,7 +50,6 @@ class WSInstrumentation {
 }
 
 object WSInstrumentation {
-  val UserTime = "UserTime"
 
   def basicRequestAttributes(request: WSRequest): Map[String, String] = {
     Map[String, String](
diff --git a/kamon-play/src/test/scala/kamon/play/WSInstrumentationSpec.scala b/kamon-play/src/test/scala/kamon/play/WSInstrumentationSpec.scala
index 0c3783bb..775d3e26 100644
--- a/kamon-play/src/test/scala/kamon/play/WSInstrumentationSpec.scala
+++ b/kamon-play/src/test/scala/kamon/play/WSInstrumentationSpec.scala
@@ -28,9 +28,9 @@ import akka.testkit.{ TestKitBase, TestProbe }
 import com.typesafe.config.ConfigFactory
 import org.scalatest.{ Matchers, WordSpecLike }
 import kamon.Kamon
-import kamon.metrics.{ TraceMetrics, Metrics }
-import kamon.metrics.Subscriptions.TickMetricSnapshot
-import kamon.metrics.TraceMetrics.ElapsedTime
+import kamon.metric.{ TraceMetrics, Metrics }
+import kamon.metric.Subscriptions.TickMetricSnapshot
+import kamon.metric.TraceMetrics.ElapsedTime
 
 class WSInstrumentationSpec extends TestKitBase with WordSpecLike with Matchers with OneServerPerSuite {