This formats all copyright comments according to SPDX formatting guidelines.
Additionally, this resolves the remaining GPLv2 only licensed files by relicensing them to GPLv2.0-or-later.
Many games report 6 channel output while only providing data for 2. We only output 2-channel audio regardless, and in the downmixing, front left/right only provide 36% of their volume. This is done assuming all of the other channels also contain valid data, but in many games they don't. This PR alters the downmixing to preserve front left/right, so volume is not lost.
This improves volume in Link's Awakening, New Super Mario Bros U, Disgaea 6, Super Kirby Clash.
Preliminary work for upmixing & general cleanup. Fixes basic issues in games such as Shovel Knight and slightly improves the LEGO games. Upmixing stitll needs to be implemented.
Audio levels in a few games will be fixed as we now use the downmix coefficients when possible instead of supplying our own
