This PR introduces Collector, a type that is composed by the same methods of Sensor, ot.Tracer and LeveledLogger, plus a few convenient methods. Collector is an implementation of the newly introduced TracerLogger interface.
It also deprecates InitSensor in favor of StartMetrics.

Why

The name "sensor" is misleading. What our tracer provides is a tracer collector.
Our tracer communicates to the Go Sensor, which is a plugin of the Instana Agent.

As we cannot delete public APIs, we then deprecate Sensor in favor of using the collector. This will happen in future PRs.

The sensor instance is still accessible via Collector.LegacySensor() and can be used for instrumentations. Exemple:

c := instana.InitCollector(&instana.Options{
	Service: "my-go-app",
})

handler := func(w http.ResponseWriter, r *http.Request) {
	fmt.Fprint(w, "Ok")
}

http.HandleFunc("/foo", instana.TracingHandlerFunc(c.LegacySensor(), "/foo", handler))

Features

• The Collector is a concrete implementation of a new interface TracerLogger.
• SensorLogger is a small interface representing all non-deprecated methods from Sensor
• The TracerLogger interface embeds Tracer and LeveledLogger and the newly introduced SensorLogger.
• It works as both Tracer and Logger, so their usage is less verbose:
  • Before: sensor.Tracer().StartSpan(...)
  • After: c.StartSpan...()
  • Before: s.Logger().Error()
  • After: c.Error()
• Usage is simpler. There is no need to provide a tracer and then provide the options. The function InitCollector expects the options as an argument
• A new Recorder option is available. It's usually used for testing, so customers shouldn't worry about setting it.
• A new method instana.StartMetrics should be used in favor of instana.InitSensor for better naming.