Implement start-to-finish on-the-fly playback for large audio files

The current SoundFile implementation decodes and loads the entire content of the audio file into RAM, which is the only reliable way to allow low-level buffer access, editing and scrubbing.

A currently unsupported use case is straightforward on-the-fly playback of long audio files that are too big to be kept in memory. This should be feasible by implementing a wrapper around the current JavaSound decoding functionality in SoundFile and packing it inside a UnitGenerator that passes the incrementally decoded audio to JSyn for immediate playback. (Pausing and restarting could even be supported, just no scrubbing/skipping or editing.)