Public issue https://github.com/mackron/miniaudio/issues/584

Updating the noise type should not be supported. An oversight on my
part. Users should reinitialize a fresh `ma_noise` object instead.

This change simply returns an error and triggers an assert in debug
mode.

Public issue: https://github.com/mackron/miniaudio/issues/585

By using the gainer to apply the master volume, we can essentially get
master volume control for free by premultiplying the per-channel
volumes by the master volume before processing.

If you were previously using this, it will no longer have any effect.
SSE2 and NEON will be used if supported, but can be disabled with
`MA_NO_SSE2` and `MA_NO_NEON`.

Maintaining AVX2 optimizations by hand is not worth the effort. The use
of AVX2 is now dependent on the compiler's auto-vectorization function.

Public issue https://github.com/mackron/miniaudio/issues/582

Public issue https://github.com/mackron/miniaudio/issues/582