Fixes OPUS_SET_GAIN (was a bug in MULT16_32_P16())
Whoa! This fixes a pretty bad fixed-point stereo regression
Fixes Opus-custom preemphasis

Also adds denorm avoidance for non-48 kHz rates
Disables assembly optimizations by default because of several problems reported
Revert "Disables assembly optimizations by default because of several problems reported"

This reverts commit 2446445b15e0a1961e1566006b34c586fd3162c4.
Start a release checklist.
Mention updating the website examples.
Bump soname
Turns a 16x32 multiply into a 16x16 one in celt_preemphasis().
Fixed-point fast-path for normal 48 kHz encoding in celt_preemphasis()