+ core: MinMaxCounter for actor mailbox size
= core: fixed ActorMetricsSpec
+ core: added MinMaxCounterSpec and new test in ActorMetricsSpec
= core: code format
+ play: upgrade version to 2.3.RC1 and change Specs2 for ScalaTests
= play: change code format
+ play: new rename trace test
+ play: removed default dispatchers to kamon default dispatcher and refactor test in WSInstrumentationSpec