onError and onTelemetry handlers

[toddhgardner]

The agent now allows you to add handlers for errors or telemetry. This allows the user or wrapping agents to manipulate things to add more data or prevent something from being sent.

TrackJS.onError((payload) => {
  return payload.entry !== "network"; // ignore all network errors
});

TrackJS.onTelemetry((type, telemetry) => {
  if (type === "con") {
    telemetry.message = telemetry.message.replace(/thing-that-looks-secret/, "SECRET");
  }
  return true;
});