OpenTelemetry Stackdriver

This crate provides an opentelemetry exporter for use with Google Stackdriver trace. It uses gRPC to send tracing spans.
Contributions are welcome.
Propagator
Feature flag propagator will enable the GoogleTraceContextPropagator which implements the TextMapPropagator trait for Google X-Cloud-Trace-Context Trace Context format.
Example usage:
set_text_map_propagator;