http.ResponseWriters may implement additional interfaces
(http.CloseNotifier, http.Flusher, http.Hijacker, http.Pusher,
io.ReaderFrom) that get lost when the ResponseWriter is wrapped in
another object. This change uses the httpsnoop package to wrap the
ResponseWriter so that the resulting object implements any of the
optional interfaces that the original ResponseWriter implements as
well as using the replacement ResponseWriter methods that gather
information for tracing.
* Remove otel/sdk dependency from grpctrace
Use otel/trace/testtrace instead and cleanup testing code.
* Update httptrace to not depend on the SDK
Update testing to use api/trace/testtrace instead.
* Add changes to Changelog
* Make the SDK its own Go module
* Upgrade go.mod to 1.14 project wide
* go mod tidy
