OpenCensus Zipkin Reporter

To use, add opencensus_zipkin dependency as a runtime application (in rebar3 this means add to the applications list of .app.src) and set as the reporter in the opencensus configuration:

{opencensus, [
    {reporters, [{oc_reporter_zipkin, [{address, "http://localhost:9411/api/v2/spans"},
                                       {local_endpoint, #{<<"serviceName">> => <<"service">>}]}}]}
    ...]}