[Openal] Memory backend and multiple instances

[Chris Robinson]

Hi.

OpenAL Soft 1.14 includes the ability to render audio to a memory buffer, 
using the ALC_SOFT_loopback extension:
http://kcat.strangesoft.net/openal-extensions/SOFT_loopback.txt

You can create as many loopback devices as you want (using 
alcLoopbackOpenDeviceSOFT), which can each have its own format+context and set 
of sources to play. You also specify when and where each device renders 
samples (using alcRenderSamplesSOFT). The format of the rendered audio is 
controlled by the attributes passed to alcCreateContext.

If there's anything more you need or aren't sure of, feel free to ask. :)