* Update License header for all source files
- Add Apache 2.0 header to source files that did not have one.
- Update all existing headers dated to 2019 to be 2020
- Remove comma from License header to comply with the Apache 2.0
guidelines.
* Update Copyright notice
Use the standard Copyright notices outlined by the
[CNCF](https://github.com/cncf/foundation/blob/master/copyright-notices.md#copyright-notices)
* Add `Span#Error` method to simplify setting an error status and message.
* `Span#Error` should no-op on nil errors
* Record errors as a span event rather than status/attributes.
The implementation in the SDK package now relies on existing API methods.
* Add WithErrorStatus() ErrorOption to allow setting span status on error.
* Apply suggestions from code review
Co-Authored-By: Krzesimir Nowak <qdlacz@gmail.com>
* Address code review feedback
* Clean up RecordError tests
* Ensure complete and unique error type is recorded for defined types
* Avoid duplicating logic under test in tests
* Move TestError to internal/testing package, improve RecordError test scenarios
Co-authored-by: Krzesimir Nowak <qdlacz@gmail.com>
