Shoutcast: Only queue metadata if it has changed
Fix Pumper Output

* Pumper: Use stream.listen to get a rewinder, then pipe that to our output
* Rewind: Add `pumpOnly` option to getRewinder, causes live playhead to not
  get hooked up
* Rewind: Rework `burstFrom` to take offset and burst seconds, and to return
  both offset and data instead of inserting the data directly
* Rewinder: Add support for providing `pump` as a number instead of just as
  a boolean
* Slave Server: Standardize call to create pumper output
* Slave Stream: Add `output` to request log