Adding changelog entries for the 0.5b0 release

Total Changelog:

Documentations has been significantly overhauled, including:

* a getting started guide
* examples has been consolidated to an docs/examples folder
* several minor improvements to the examples in each extension's readme.

- Adding Correlation Context API and propagator
  ([open-telemetry#471](open-telemetry#471))
- Adding a global configuration module to simplify setting and getting
  globals
  ([open-telemetry#466](open-telemetry#466))
- Rename metric handle to bound metric
  ([open-telemetry#470](open-telemetry#470))
- Moving resources to sdk
  ([open-telemetry#464](open-telemetry#464))
- Implementing propagators to API to use context
  ([open-telemetry#446](open-telemetry#446))
- Implement observer instrument for metrics
  ([open-telemetry#425](open-telemetry#425))
- Adding named meters, removing batchers
  ([open-telemetry#431](open-telemetry#431))
- Renaming TraceOptions to TraceFlags
  ([open-telemetry#450](open-telemetry#450))
- Renaming TracerSource to TraceProvider
  ([open-telemetry#441](open-telemetry#441))

- Adding Correlation Context SDK and propagator
  ([open-telemetry#471](open-telemetry#471))
- Adding OT Collector metrics exporter
  ([open-telemetry#454](open-telemetry#454))
- Improve validation of attributes
  ([open-telemetry#460](open-telemetry#460))
- Re-raise errors caught in opentelemetry.sdk.trace.Tracer.use_span()
  (open-telemetry#469)
  ([open-telemetry#469](open-telemetry#469))
- Adding named meters, removing batchers
  ([open-telemetry#431](open-telemetry#431))
- Make counter and MinMaxSumCount aggregators thread safe
  ([open-telemetry#439](open-telemetry#439))

- Initial release. Support is included for both trace and metrics.

ext/opentelemetry-ext-otcollector/CHANGELOG.md

@@ -2,3 +2,4 @@
 
 ## Unreleased
 
+## 0.5b0

opentelemetry-api/CHANGELOG.md

@@ -2,6 +2,27 @@
 
 ## Unreleased
 
+## 0.5b0
+
+- Adding Correlation Context API and propagator
+  ([#471](https://github.com/open-telemetry/opentelemetry-python/pull/471))
+- Adding a global configuration module to simplify setting and getting globals
+  ([#466](https://github.com/open-telemetry/opentelemetry-python/pull/466))
+- Rename metric handle to bound metric
+  ([#470](https://github.com/open-telemetry/opentelemetry-python/pull/470))
+- Moving resources to sdk
+  ([#464](https://github.com/open-telemetry/opentelemetry-python/pull/464))
+- Implementing propagators to API to use context
+  ([#446](https://github.com/open-telemetry/opentelemetry-python/pull/446))
+- Adding named meters, removing batchers
+  ([#431](https://github.com/open-telemetry/opentelemetry-python/pull/431))
+- Renaming TraceOptions to TraceFlags
+  ([#450](https://github.com/open-telemetry/opentelemetry-python/pull/450))
+- Renaming TracerSource to TraceProvider
+  ([#441](https://github.com/open-telemetry/opentelemetry-python/pull/441))
+- Adding attach/detach methods as per spec
+  ([#429](https://github.com/open-telemetry/opentelemetry-python/pull/450) 
+
 ## 0.4a0
 
 Released 2020-02-21

opentelemetry-sdk/CHANGELOG.md

@@ -2,6 +2,21 @@
 
 ## Unreleased
 
+## 0.5b0
+
+- Adding Correlation Context SDK and propagator
+  ([#471](https://github.com/open-telemetry/opentelemetry-python/pull/471))
+- Adding OT Collector metrics exporter
+  ([#454](https://github.com/open-telemetry/opentelemetry-python/pull/454))
+- Improve validation of attributes
+  ([#460](https://github.com/open-telemetry/opentelemetry-python/pull/460))
+- Moving resources to sdk
+  ([#464](https://github.com/open-telemetry/opentelemetry-python/pull/464))
+- Re-raise errors caught in opentelemetry.sdk.trace.Tracer.use_span()
+  ([#469](https://github.com/open-telemetry/opentelemetry-python/pull/469))
+- Implement observer instrument
+  ([#425](https://github.com/open-telemetry/opentelemetry-python/pull/425))
+
 ## 0.4a0 
 
 Released 2020-02-21