This is a first official beta release, which provides almost fully complete metrics, tracing, and context propagation functionality.
There is still a possibility of breaking changes.

Added

• Add Observer metric instrument. (#474)
• Add global Propagators functionality to enable deferred initialization for propagators registered before the first Meter SDK is installed. (#494)
• Simplified export setup pipeline for the jaeger exporter to match other exporters. (#459)
• The zipkin trace exporter. (#495)
• The OTLP exporter to export metric and trace telemetry to the OpenTelemetry collector. (#497) (#544) (#545)
• The StatusMessage field was add to the trace Span. (#524)
• Context propagation in OpenTracing bridge in terms of OpenTelemetry context propagation. (#525)
• The Resource type was added to the SDK. (#528)
• The global API now supports a Tracer and Meter function as shortcuts to getting a global *Provider and calling these methods directly. (#538)
• The metric API now defines a generic MeterImpl interface to support general purpose Meter construction.
  Additionally, SyncImpl and AsyncImpl are added to support general purpose instrument construction. (#560)
• A metric Kind is added to represent the MeasureKind, ObserverKind, and CounterKind. (#560)
• Scripts to better automate the release process. (#576)

Changed

• Default to to use AlwaysSampler instead of ProbabilitySampler to match OpenTelemetry specification. (#506)
• Renamed AlwaysSampleSampler to AlwaysOnSampler in the trace API. (#511)
• Renamed NeverSampleSampler to AlwaysOffSampler in the trace API. (#511)
• The Status field of the Span was changed to StatusCode to disambiguate with the added StatusMessage. (#524)
• Updated the trace Sampler interface conform to the OpenTelemetry specification. (#531)
• Rename metric API Options to Config. (#541)
• Rename metric Counter aggregator to be Sum. (#541)
• Unify metric options into Option from instrument specific options. (#541)
• The trace API's TraceProvider now support Resources. (#545)
• Correct error in zipkin module name. (#548)
• The jaeger trace exporter now supports Resources. (#551)
• Metric SDK now supports Resources.
  The WithResource option was added to configure a Resource on creation and the Resource method was added to the metric Descriptor to return the associated Resource. (#552)
• Replace ErrNoLastValue and ErrEmptyDataSet by ErrNoData in the metric SDK. (#557)
• The stdout trace exporter now supports Resources. (#558)
• The metric Descriptor is now included at the API instead of the SDK. (#560)
• Replace Ordered with an iterator in export.Labels. (#567)

Removed

• The vendor specific Stackdriver. It is now hosted on 3rd party vendor infrastructure. (#452)
• The Unregister method for metric observers as it is not in the OpenTelemetry specification. (#560)
• GetDescriptor from the metric SDK. (#575)
• The Gauge instrument from the metric API. (#537)

Fixed

• Make histogram aggregator checkpoint consistent. (#438)
• Update README with import instructions and how to build and test. (#505)
• The default label encoding was updated to be unique. (#508)
• Use NewRoot in the othttp plugin for public endpoints. (#513)
• Fix data race in BatchedSpanProcessor. (#518)
• Skip test-386 for Mac OS 10.15.x (Catalina and upwards). #521
• Use a variable-size array to represent ordered labels in maps. (#523)
• Update the OTLP protobuf and update changed import path. (#532)
• Use StateLocker implementation in MinMaxSumCount. (#546)
• Eliminate goroutine leak in histogram stress test. (#547)
• Update OTLP exporter with latest protobuf. (#550)
• Add filters to the othttp plugin. (#556)
• Provide an implementation of the Header* filters that do not depend on Go 1.14. (#565)
• Encode labels once during checkpoint.
  The checkpoint function is executed in a single thread so we can do the encoding lazily before passing the encoded version of labels to the exporter.
  This is a cheap and quick way to avoid encoding the labels on every collection interval. (#572)
• Run coverage over all packages in COVERAGE_MOD_DIR. (#573)

Changes since v0.2.3

a1c2439 Prepare for releasing v0.3.0 (#578)
a15e507 Scripts for releasing. (#576)
7623fc5 Remove GetDescriptor (#575)
c95360f Run coverage over all packages beneath COVERAGE_MOD_DIR (#573)
cc756f6 Encode labels once during checkpoint (#572)
f7df68b Add support for Resources in the SDK (#552)
a01f63b Replace Ordered with an iterator in export.Labels. (#567)
d8682c1 Refactor the SDK helpers, create MeterImpl (#560)
e0406dd Provide an implementation of the Header* filters that does not depend on go1.14 (#565)
80b720a update stdout trace with resource. (#558)
435c39a Update OTLP exporter with latest proto (#550)
74a5285 update jaeger exporter to translate resources to tags. (#551)
2ef25ea Add filters for othttp plugin (#556)
217a97d Replace ErrNoLastValue and ErrEmptyDataSet by ErrNoData (#557)
6ada85a (resource_zipkin, go_114) add resource option to Provider. (#545)
638b865 Update Sampler descriptions (#511)
cba1664 Add metrics support to the OTLP exporter (#544)
fcc4aca Fix typo in module name (#548)
8680783 Use StateLocker in MinMaxSumCount (#546)
46ac030 Eliminate goroutine leak in histogram stress test (#547)
2ccddfe Update README with import instructions and how to build / test (#505)
23e65ac Remove metric options; rename "counter" aggregator to "sum" (#541)
d9210f5 Zipkin exporter (#495)
4047c08 Introduce metric constructor errors, MeterMust wrapper (#529)
288821c Make histogram aggregator checkpoint consistent (#438)
ae9033e Use a variable-size array to represent ordered labels in maps (#523)
8575142 add shorter version for global providers (#538)
9674c81 Drop the gauge instrument (#537)
fe0099f [tracing] add simplified export pipeline setup for Jaeger (#459)
8cddf30 Context propagation in opentracing bridge (#525)
7a1cbbc Update Samplers to conform to Spec (#531)
af54288 Update OTLP protos, fix imports (#532)
1ff0f2a add resource type. (#528)
3bf3927 Add status message parameter (#524)
5850278 opentelemetry collector trace exporter (#497)
9459629 Remove the StackDriver trace exporter (#452)
43db6ec Propose putting isobel to emeritus :( (#526)
79de90a fix data race in BatchedSpanProcessor (#518)
161556a Update provider to use AlwaysSampler instead of ProbabilitySampler (#506)
20ecc38 skip test-386 for Mac OS 10.15.x (Catalina and upwards). (#521)
a202f16 Add observer metric (#474)
547d584 Add global propagators (#494)
6769330 use NewRoot() standard code. (#513)
148c9ce Make the default label encoding unique (#508)