add support for head-shadow/penumbra filter for positional audio streams

When positional audio sources are behind the listener, we selectively apply low-pass filtering to simulate a HRTF.   Feature may be enabled/disabled using the new audio-mixer settings in domain server. 
ok - so this is a combo of three things coding standard related.

1) no spaces after ( or before )
2) BUT do include spaces around operators like * so... "a0 * scale"
3) always include a space after a comma