Define what is measured instead of all inside the Task

[chriswalpen]

It should be possible to define which part of a Task is measured instead of measuring the whole task.

When measuring webrequests, it should be possible to only measure the time the request takes.

.Task(ctx => {
  // this is not measured
  ctx.Measure(() => {
    // do stuff to measure here
  });
  // this is not measured
});