* Support updated OT 0.14 / tracing-OT 0.12 crate versions
Add support for opentelemetry 0.14 and tracing-opentelemetry 0.13.
Make corresponding changes to the features, docs, and examples.
Due to the use of two different versions of the same packages, some
reorganization had to be done for the internal modules.
Addresses issue #22.
* Re-export versioned set_otel_parent `fn`s for use in macro
* Add http.route.
* Align all fields with OpenTelemetry's semantic conventions.
* Add span kind.
* Emit event for errors.
Add OTEL status code.
* Create otel.status_code field as empty.
* Fix errors.
* Add (feature-gated) support for OpenTelemetry span propagation.
* Capture the trace id as an attribute on the span.
* Change message.
* Log the newly-generated trace id if there is no parent context.
* Define a root_span macro as a stepping stone to allow crate users to add their own fields to the root span.
* Add comments.
* mut is no longer necessary.
* Allow users to customise generation of the root span. Split recording fields on span end from emission of log record. Make log record on error optional via feature flag.
* Provide constructor + default implementation.
* Explode into multiple modules.
Fix various paths/private imports in root_span.
* Rename module to root_span_macro.
* Add a new extractor to retrieve the root span.
* Document crate.
* Docs!
* Add section on OTEL.
* Mention actix-web-opentelemetry.
* Add OpenTelemetry example.
* Improve readme.
* Add custom root span example.
Co-authored-by: LukeMathWalker <contact@palmieri.com>
