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

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

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

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

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`.