* Fixed my old stupid bug that disabled sound after having played the
    first playlist item.
  * Added `Prev' and `Next' buttons to the interface, with the beginning of
    a playlist window (still empty).
  * Added `Slow' and `Fast' buttons to the interface and popup menu.

  Ok, I promise it's the last time I check bloat in, from now the interface
  commits will be much cleaner and actually fix things :)