* Added: opentracing to gemspec.

* Added: Opentracing CI tasks.

* Added: Datadog::OpenTracer module.

* Added: Datadog::OpenTracer spec helpers.

* Added: Datadog::OpenTracer::Tracer.

* Added: Datadog::OpenTracer::Span.

* Added: Datadog::OpenTracer::SpanContext.

* Added: Datadog::OpenTracer::Scope.

* Added: Datadog::OpenTracer::ScopeManager.

* Added: Datadog::OpenTracer::Carrier.

* Added: Datadog::OpenTracer::Tracer#datadog_tracer.

* Added: Patch for OpenTracing#global_tracer=.

* Added: Datadog::OpenTracer::SpanContext implementation.

* Added: Datadog::OpenTracer::Span implementation.

* Changed: Bump required Ruby version for OpenTracing to 2.1.

* Added: Datadog::OpenTracer::SpanContextFactory.

* Changed: OpenTracer::Span#set_baggage_item to create new SpanContexts.

* Changed: Datadog::OpenTracer::SpanContext#baggage to be immutable.

* Added: span_id, trace_id, parent_id to Datadog::OpenTracer::SpanContext.

* Changed: Replaced span_id, trace_id, parent_id with reference to Datadog::Context.

* Changed: Scope to expect Span and ScopeManager.

* Added: Datadog::OpenTracer::ThreadLocalScope and Manager.

…490)

 * Fixed: ThreadLocalScopeManager not passing finish_on_close to scope.

 * Added: Implementation for OpenTracer::Tracer

 * Added: OpenTracing::Tracer integration specs.

* Added: Propagators to OpenTracer.

* Added: Specs for OpenTracer::Propagators.

* Fixed: OpenTracer::Tracer#start_span not using provided SpanContext.

* Added: OpenTracer context propagation integration specs.

* Fixed: Rack headers as symbols incompatible with OpenTracer propagation.

* Fixed: Text map baggage as symbols incompatible with OpenTracer propagation.

…#518)

* Fixed: OpenTracer::Tracer not using child_of SpanContext properly.

* Changed: OpenTracer to append its spans to Datadog auto-instrumentation.

…an IDs. (#539)