WIP: Move HLS Segmenter into Master

* Move HLS Segmenting into Master; Slave will simply take segment list
  snapshots to serve indices and segments.
* HLSSegmenter: Throw out how we were numbering segment sequence. Move to a
  zero-based sequence with memory in the rewind dump. Add discontinuity
  sequence.
* HLSSegmenter: Rebuild audio flow, adding Injector and Finalizer streams
HLS: Early support for segment playback using RewindBuffer

* Instead of separately transmitting segment data from master -> slave, use
  the timestamp information in the segment snapshot to look up the data in
  the RewindBuffer and play it from there.
* Fix timestamp handling in hls snapshot transit
* FIXME: RewindBuffer's `findTimestamp` -> `pumpFrom` isn't precise enough for
  this task, resulting in occasional audio mishits. That lookup will need to
  be tightened up.