Audio support for Vapoursynth plugin

[adworacz]

Since it's been a few years since VS added support for audio, it would be great to match the AVS plugin's audio support.

[msg7086]

I got a quick implementation but need to get #133 reviewed first, an issue found during porting code to VS.

[msg7086]

Fixed in #135, though more fixes are coming in after that, before we can release a new build.

[adworacz]

Sounds great, thanks for the updates.