Releasing v0.4.0 (open-telemetry#1128)

Enable publishing releases from tags (open-telemetry#749)

Circle was not running any builds for tags because the publish job had
other jobs as dependencies and they did not explicitly specify that they
should be run for tags. Looks like Circle will always run a job for any
branch unless the branch is ignored and never run a job for a tag unless
the tag is explicitly enabled.

Co-authored-by: Bogdan Drutu <[email protected]>

Enable publishing releases from tags (open-telemetry#749)

Circle was not running any builds for tags because the publish job had
other jobs as dependencies and they did not explicitly specify that they
should be run for tags. Looks like Circle will always run a job for any
branch unless the branch is ignored and never run a job for a tag unless
the tag is explicitly enabled.

Co-authored-by: Bogdan Drutu <[email protected]>

testing ci tiggers

Refactor component and factory interface definitions (open-telemetry#683

)

As we are preparing for Beta release we want to cleanup publicly exported
types and interfaces and do all necessary refactoring and breaking changes
now, before the Beta release. We will have a lot less leeway for breaking
changes after the Beta release.

Component related type declarations are now all in the `component` package.
This makes it possible for the interfaces to reference each other. This
was were very restricted earlier because component interfaces were in 5
different packages and many proposals were impossible to implement because
they would result in circular dependencies between packages.

(An example upcoming new capability that is enabled by this refactoring
is for components to query the Host for other components and for factories).

List of changes in this commit:

- Move all factory interfaces and component interfaces to component package.
- Rename old factories and components interfaces to use "Old" suffix for clarity.
- Eliminate forced checks that components implement factories. This is already
  enforced by the compiler when the factory is added to the Defaults() and
  was unnecessary code.
- Eliminated some unnecessary codes (removed overall over 200 lines).
- Run `go mod tidy` on testbed.

Warning: this is a breaking change to publicly exported types and function
signatures. We announced that a breaking change is comming. Once we agree
to merge this commit we will need to announce the exact list of changes
and guide component authors to modify their components accordingly.

Future changes:
- Once all components are migrated to the new internal representation,
  delete all "Old"-suffixed definitions. This will likely be done while
  we are still in Beta phase, before the Stable release.

Disable usage msg after Start and suppress known errors from logginge…

…xporter (open-telemetry#638)

Two fit and finish issues on this change:
- With the improved shutdown merged recently the Collector started to show error messages on shutdown.
- Call to Sync on loggingexporter generates non-actionable error messages.

Add OTLP trace data types, factories and helpers (open-telemetry#534)

This is step one in converting in-memory representation from OC to OTLP. This
change has no effect except in tests. The introduced code is not reachable.

Issue: open-telemetry#478

Add regexp support to service name include/exclude filters (open-tele…

…metry#522)

- Added regexp support to service name field in include/exclude
  filters of attributes processor. This makes it consistent with
  span name fields which already use regexp patterns.

- Added match_type to make service name and span name matching explicit.

Testing: added unit and E2E tests.
Documentation: README modified as appropriate.

Add support for CONSUMER and PRODUCER span kinds (open-telemetry#520)

Previously these span kinds were not supported because OpenCensus
does not have equivalent span kinds and they were translated as
"Unspecified" span kind when received by Zipkin receiver.

Now these span kinds are internally stored in a span attribute
named "span.kind" when received by Zipkin receiver. When exporting,
this attribute is used to perform a reverse translation in Zipkin
exporter. "span.kind" also matches the OpenTracing semantic
conventions so it should be correctly interpreted by any backend
that follows this convention.

## To reviewers:
The code that does translation from OC to Zipkin is moved from
exporter/zipkinexporter/zipkin.go to translator/trace/zipkin/protospan_to_zipkinv1.go.
protospan_to_zipkinv1.go is not all new code, only the code that
deals with span kind is to be reviewed.

Testing done:
- Added a unit test to verify translations between Zipkin,OC and Jaeger.
- TODO: Add E2E test to verify these translations on real pipelines.

Add a memory limiter processor (open-telemetry#498)

This adds a processor that drops data according to configured memory limits.
The processor is important for high load situations when receiving rate exceeds exporting
rate (and an extreme case of this is when the target of exporting is unavailable).

Typical production run will need to have this processor included in every pipeline
immediately after the batch processor.