opusenc: implement a psychoacoustic system

opusenc: implement a psychoacoustic system

This commit implements a psychoacoustic system for the native Opus
encoder. Its unlike any other psychoacoustic system known since its
capable of using a lookahead to make better choices on how to treat the
current frame and how many bits to allocate for it (and future frames).

Also, whilst the main bulk of the analysis function has to run in a
single thread, the per-frame anaylsis functions does not modify the main
psychoacoustic context, so in the future it will be fairly trivial to
run those as slice threads.

Signed-off-by: Rostislav Pehlivanov <atomnuker@gmail.com>