* 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
* Add golint to linters and resolve issues.
I decided to remove constructors for some of the propagation types
because the constructors can be reduced to either using the zero value
or a single, non optional member.
* Enable gofmt and commit fixes