* 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
* add tests for api/trace/current.go
* add interface validaion for type: mockSpan
* rework for exported NoopSpan and ditch useless tabletest for TestSetCurrentSpan()
* 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
* fix compile errors.
* fix lint errors.
* add circle-ci job.
* rename IDHigh to TraceIDHigh
* rename the file.
* add go get for goimports and golangci-lint
* enable GO111MODULE and remove comments.
* remove working dir and update cache name
* Add TEST_RESULT env back.
* run go mod tidy.
* remove go mod download.
* add test coverage.
* fix TraceID.
* fix circlefi config error.
* remove install-tools.
* remove ALL_TEST_SRC from Makefile.
* 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.
