* add propagation api.
* add http propagator interface and w3c propagator implementation.
* remove Extract api from trace.
* remove Extract interface for tracer.
* fix copyright.
* fix variable names and comments.
* move inject/extract out of trace.
* replace INVALID_SPAN_CONTEXT with EmptySpanContext function.
* fix tag.Map.
* make carrier as interface instead of http.Request.
* rename structs and update doc comments..
* add doc.go
* update doc.
* add noop propagator.
* add new propagation api with Supplier interface.
- added Default Tracer which simply propagates SpanContext.
- added CopyOfRemote option to simply create remote span.
* remove old propagator.
* rename propagator to TextFormatPropagator.
* rename default tracer/span as pass_through tracer/span.
* add test for pass through tracer.
* add missing interface to pass through tracer.
* return SpanContext instead of contex.Context from Extract interface.
- also remove PassThroughTracer
* fix review comments.
* add more test cases for traceContext extraction.
* remove tidy temporarily from circle-ci target to avoid build failure.
* allow header ending in dash '-'.
* add inject test for non-zero value other than 01 for traceoption
* add AddLink and Link interface to MockSpan
* fix running go mod tidy on every build.
* Merge two event methods in span API
There was an agreement to get rid of the Event interface and
consolidate the two methods for adding events into one. See #57.
* Eliminate the use of the Event interface
There is no need for the SDK to provide the implementation of the
Event interface - it is used nowhere.
* Drop the Event interface
It's dead code now.
* Make it possible to override a finish timestamp through options
Opentracing to opentelemetry bridge will certainly use this feature.
* Obey the start time option
* Add tests for events and custom start/end times
* Move scope.Active to trace.CurrentSpan
* Remove scope / does not build
* Global tracer
* Checkpoint
* Checkpoint
* Add key/key.go for key.New
* Comments
* Remove more EventID and ScopeID
* Use Handle to describe static objects
* TODOs
* Remove empty file
* Remove singletons
* Update TODOs
* TODO about map update
* Make stats package option aliases (like key has)
* Rename experimental/streaming
* streaming SDK builds w/ many TODOs
* Get the examples building
* Tidy up metric API / add interface check
* Remove logic from the registry; this is now a placeholder
* rename Log and Logf interface to AddEvent and AddEventf.
- also remove log package.
* provide only AddEvent interface to Span
- Event can be created using Event specific interface.
* add var trick for Event interface.
