Instead of the legacy SDL_OpenAudio() method, we now use the newer
SDL_OpenAudioDevice() functions. This fixes audio in Windows if the SDL
version is 2.0.6 or higher.
It also allows us to use 48kHz audio for Windows (96kHz somewhat works
too, but since we don't get absolutely smooth audio with it, I'd stick
with 48kHz for now until we find a solution. 44.1Khz is available as
fallback for SDL 2.0.5 and lower. Yes, the 2.0.5 to 2.0.6 transition was
quite harsh in terms of Windows audio support...
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