Add multi-channel (single file) or multi-track (multi file per track/channel) audio recording capability

[dts24436]

Not sure if it is feasible, but I've been doing the game recording for at least 7 times to get the following files:

1. an AVI file with a mono audio track of all audio channels downmixed,
2. 6 mono PCM WAV files for all the 5 individiual audio channels, and all the other channels aside them,

so that I can mix them afterwards in 2-channel stereo or certain surround layouts.

All these procedures had been done using versions 2.2.2 and 2.2.3 before.

Therefore to put forth the idea of making multi-channel or multi-track audio recording during AVI or WAV recording:

1. If the existing audio channels of the NES/FC core is too many for a single WAV file to contain well, multiple 1-channel WAV files for all channels each could be produced instead.
2. If the existing audio channels of the NES/FC core is too many for a single AVI file to contain well, it'll be better to simultaneously produce multiple 1-channel WAV files for all channels each aside the AVI which contains a mono audio track already downmixed.

e.g. Glad to see in the version 2.6.4, the RGB color mapping of the output AVI file being x264 lossless is corrected, and the problem of 96kHz audio (16-bit highest quality) not able to be written into the AVI file is also fixed.