Adding NoopScope, TestScope and Sanitizer

[ravirajj]

This pull request contains the following commits to bring uber-java/tally on par with uber-go/tally:

• Upgrade to Java 8 (previous attempt #39)
  • enable the use of static interface methods to hide implementation classes.
  • remove synchronized statements and enable the use of ConcurrentMap.putIfAbsent.
• Only exposing public interfaces, implementations are package-private:
  • Moving BucketPairImpl.bucketPairs() to BucketPairs.create().
• Adding NoopScope (previous attempt #40), NullStatsReporter
• Adding TestScope interface and factory methods
• Adding Sanitizer interface and implementation

[JigarJoshi]

Repeats the features from

https://github.com/uber-java/tally/pull/39 https://github.com/uber-java/tally/pull/40

[andrewmains12]

Only exposing public interfaces, implementations are package-private.

This is unfortunately probably backwards incompatible, and I'm not sure worth a new version. Should we back that out? cc @prateek

[ravirajj]

Only exposing public interfaces, implementations are package-private.

This is unfortunately probably backwards incompatible, and I'm not sure worth a new version. Should we back that out? cc @prateek

The main change here is moving BucketPairImpl. bucketPairs() to BucketPairs.create(), since Java 8 allows you to add static methods to interfaces. Alternatively, we can add BucketPairFactory.createbucketPairs() if we are using Java 7 and hide the *Impl classes.

[ravirajj]

Repeats the features from #39 Plus other changes to make Travis pass! #40 Different Implementation. This implementation uses NullStatsReporter just like uber-go/tally: https://github.com/uber-go/tally/blob/master/scope.go#L32