Adds conformance test #61
                
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We have implemented a conformance test which validates a tracer's inject/extract carrier format. There is a conformance harness that sends a set of carriers to a client (written in python here) and reads the clients response from stdout.
The client reads a JSON blob from stdin, extracts the span context for each carrier format, then injects the span contexts into a new JSON blob and sends that over stdout.
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