* api(trace): change trace id to byte array.
* fix lint errors
* add helper to create trace id from hex and improve stdout exporter.
* remove comma.
* fix lint
* change TraceIDFromHex to be compliant with w3 trace-context
* revert remove of hex16 regex because its used to parse SpanID
* lint
* fix typo
* trace sdk initial commit.
* fix imports and comments.
* remove tracestate
* split trace.go
* add attribute over limit test.
* add comments and restructure span.go and tracer.go
* refactor MessageEvent
* defer unlock
* some more cleanup in span.go
* rename *MessageEvent* to *Event*
* cleanup comments in trace_test.go
* fix typos.
* return full string ID for traceID and spanID.