Audio Buffer Saving and VRC7 Audio Savestate Fix

[Dwedit]

• Clean audio when saving and loading state at zero Run-Ahead frames, via saving and restoring the audio buffer state.
• Clean audio when saving and loading state for Konami VRC7 sound
• Select between Nonlinear and Linear mixer mode. Nonlinear is more accurate to hardware, but Linear has louder DMC samples.
• Select between audio EQ modes: "Nes" (default), "Famicom" (treble diminished), "TV", "Flat" (minimal eq), "Crisp" (treble boost), and "Tinny" (treble and bass diminished).
• Nonlinear mixer mode has been made the default mixing mode. It sounds different than Linear, has quieter DMC samples, and may sound worse in some cases, but is truer to actual hardware.
• APU channels and Mapper audio now apply their initial volume levels to the output buffer immediately when loading state.
• Fixed a bug where loading state did not initialize some variables

[Dwedit]

Just realized I should ensure the added variables are initialized properly...

[inactive123]

Awesome stuff. Merging.

[Dwedit]

hold on, I caught a bug, nonlinear audio is borked at 0 runahead frames (but works otherwise), linear audio is fine at 0 runahead frames. Will submit another pull once I have it cleared up.

Edit: Appears that the bug only happened during my post-submission code cleanup, not in the actual submission. Have also fixed my local copy's bug...