* 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.
