Pause tailing the file

Nobody has claimed this yet.

Hi,

I wonder if it would be possible to include a pause and resume method.

I am assuming that it should be fairly simple:

```javascript
pause() {
if (this[kQuitting]) return

clearTimeout(this[kPollTimer])
this.paused = true
}

async resume() {
if (!this.paused) return

this[kStartPos] = null
this.paused = false

this._pollFileForChanges()
}
```

Side quesion: Is the assumption correct that I always (also for the pause/resume case above) get a `flush` event before any data, therefore I am always able to get `lastReadPosition` first (I need the exact start byte for each chunk).

Start by reading the existing tailing implementation around _pollFileForChanges, kPollTimer, kStartPos, and the flush event behavior. Add pause and resume behavior as described, and verify that resumed reads preserve the expected starting position and event ordering.

Written by the indexing model from the issue text.