The library creates a configured tracer instance.
-ToDO: configuration...
## Usage
span := opentracing.GlobalTracer().StartSpan("go test span", opentracing.ChildOf(context))
```
+## Configuration
+
+The trace library currently supports only [Jaeger](https://www.jaegertracing.io/) [golang client](https://github.com/jaegertracing/jaeger-client-go) tracer implementation.
+The configuration is done using environment variables:
+
+| environment variable | values | default |
+| ---------------------------- |------------------------------------ | -------------- |
+| TRACING_ENABLED | 1, true, 0, false | false |
+| TRACING_JAEGER_SAMPLER_TYPE | const, propabilistic, ratelimiting | const |
+| TRACING_JAEGER_SAMPLER_PARAM | float | 0.001 |
+| TRACING_JAEGER_AGENT_ADDR | IP addr[:port] | 127.0.0.1:6831 |
+| TRACING_JAEGER_LOG_LEVEL | all, error, none | none |
+
+Meaning of the configuration variables is described in Jaeger web pages.
+By default a no-op tracer is created.
+
+
## Unit testing
GO111MODULE=on go mod download