FromGRPCRequest returns a grpc RequestFunc that tries to join with an OpenTracing trace found in `req` and starts a new Span called `operationName` accordingly.

FromHTTPRequest returns an http RequestFunc that tries to join with an OpenTracing trace found in `req` and starts a new Span called `operationName` accordingly.

ToGRPCRequest returns a grpc RequestFunc that injects an OpenTracing Span found in `ctx` into the grpc Metadata.

ToHTTPRequest returns an http RequestFunc that injects an OpenTracing Span found in `ctx` into the http headers.

TraceClient returns a Middleware that wraps the `next` Endpoint in an OpenTracing Span called `operationName`.

TraceServer returns a Middleware that wraps the `next` Endpoint in an OpenTracing Span called `operationName`.