v0.17.0 Release

• Add AttributeValueDouble to AttributeValue.
• Add createWithSender to JaegerTraceExporter to allow use of HttpSender
  with extra configurations.
• Add an API Functions.returnToString().
• Migrate to new Stackdriver Kubernetes monitored resource. This could be a breaking change
  if you are using gke_container resources. For more info,
  https://cloud.google.com/monitoring/kubernetes-engine/migration#incompatible
• Add an util artifact opencensus-contrib-dropwizard to translate Dropwizard metrics to
  OpenCensus.
• Add Gauges (DoubleGauge, LongGauge, DerivedDoubleGauge, DerivedLongGauge) APIs.
• Update opencensus-contrib-log-correlation-log4j2 and
  opencensus-contrib-log-correlation-stackdriver to match the
  OpenCensus log correlation spec
  and remove all ExperimentalApi annotations.
• The histogram bucket boundaries (BucketBoundaries) and values (Count and Sum) are no longer
  supported for negative values. The Record API drops the negative value and logs the warning.
  This could be a breaking change if you are recording negative value for any measure.
• Remove support for min/max in the stats Distribution to make it compatible with Metrics.
• Dependency updates.