Rewrite Frotz audio system core

Rewrite Frotz audio system core

Introduce an audio manager which works on audio streams which are loaded into
one of several audio voices. These streams are loaded into memory in the
interperter thread and then incrementally translated to samples in the audio
thread. Multiple concurrent voices is normal during operation and should not
cause issues. Overhead when no voices are playing should be low, though as the
audio thread will be running in the background after it has been initialized,
the overhead will be non-zero.

The provided work is C89 compliant (according to GCC), is available under a
dual GPLv2+ and MIT license, and as a result of the stream loaded approach
removes the libvorbis dependency as libsndfile handles in-memory OGG files.