opus

Use a table for PVQ encoding/decoding.

58.4% speedup (2.4x faster) on test_unit_cwrs32 (no custom modes).
Gives a 3.2% speedup on
 ./opus_demo restricted-lowdelay 48000 2 96000 comp48-stereo.sw /dev/null
 on a 600 MHz Cortex A8.