Opencensus

Released 2019-04-11

- Allow for metrics with empty label keys and values
([611](https://github.com/census-instrumentation/opencensus-python/pull/611),
[614](https://github.com/census-instrumentation/opencensus-python/pull/614))

Released 2019-04-08

- Multiple bugfixes
- Use separate context package instead of threadlocals for execution context
([573](https://github.com/census-instrumentation/opencensus-python/pull/573))

Released 2019-03-11

- Fix gRPC client tracer reuse bug
([539](https://github.com/census-instrumentation/opencensus-python/pull/539))
- Update prometheus client and fix multiple bugs in the exporter
([492](https://github.com/census-instrumentation/opencensus-python/pull/492))
- Remove min and max from `Distribution`
([501](https://github.com/census-instrumentation/opencensus-python/pull/501))
- Replace stackdriver `gke_container` resources, see the [GKE migration
notes](https://cloud.google.com/monitoring/kubernetes-engine/migration#incompatible)
for details
- Componentize the package distribution. All [contrib
packages](https://github.com/census-instrumentation/opencensus-python/tree/master/contrib/)
are now decoupled from the core library, and can be released separately.

Released 2019-01-18

- Fix multiple stackdriver and prometheus exporter bugs
- Increase size of trace batches and change transport behavior on exit
([452](https://github.com/census-instrumentation/opencensus-python/pull/452))

Released 2019-01-16

- Fix a bug in the stackdriver exporter that caused spans to be exported
individually
([425](https://github.com/census-instrumentation/opencensus-python/pull/425))
- Add this changelog