progress->offset event, new progress and speed events, added fullPath to...

1. Renamed `progress` event to `offset` (as this is what it emits)
2. Added `fullPath` to tags
3. Added a new `progress` event, new  `progressiv` option with default of 200ms. It indicates how often the event should be emitted. Handy for progressbars.
4. Added `speed` event, emits bytes read per second
5. Added `pause`, `resume` and  `abort` events