Until now, Mixer not only was responsible for rendering audio buffers
but also managed writing them to audio backend (through a FIFO) and
handled various quality related parameters.
All this functionality has been moved into the new AudioOutputContext
class. It glues together AudioBackend (formerly called AudioDevice),
global quality settings and the Mixer.
The AudioOutputContext class creates a FifoWriter which calls
Mixer::renderNextBuffer() and writes the output into the BufferFifo of
the AudioOutputContext it belongs to. The BufferFifo is read by the
according AudioBackend which belongs to the AudioOutputContext as well.
The AudioOutputContext also handles resampling in case the AudioBackend
wants the buffers in a different samplerate.
During this rewrite the Mixer class and the according source files have
been renamed from "mixer" to "Mixer". This results in small changes
all over LMMS' code base.
This reverts commit c517f1fa5a.
The commit was not very helpful and introduced new xrun problems.
Instead I'll be rewriting the part of LMMS where Mixer, Mixer's
quality settings, Buffer FIFO and AudioDevice are sticked together.
There's really no need to allocate a buffer each period, push it to the
FifoBuffer and free it when fetching the buffer in
AudioDevice::getNextBuffer(). Instead keep the pointer in FifoBuffer's
pool and reuse it.
